Piezoelectric/electrostrictive device

ABSTRACT

A piezoelectric/electrostrictive including a pair of mutually opposing vibration plates, each having a first portion and a second portion, a fixation section joined to the first portion of each of the vibration plates, and at least one piezoelectric/electrostrictive element arranged on at least one of the vibration plates. A surface of the device between the fixation section and the second portion of at least one of the vibration plates is curved.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/964,221, filed Oct. 13, 2004, now U.S. Pat. No. 6,933,658, which inturn is a continuation of U.S. application Ser. No. 10/281,373, filedOct. 25, 2002, now U.S. Pat. No. 6,817,072, which in turn is a divisionof U.S. application Ser. No. 09/676,209, filed Sep. 29, 2000, now U.S.Pat. No. 6,534,899, which claims the benefit under 35 USC §119(e) ofU.S. Provisional Application Ser. No. 60/204,702, filed May 16, 2000,and is a continuation of U.S. application Ser. No. 09/524,042, filedMar. 13, 2000, now U.S. Pat. No. 6,498,419, the entireties of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a piezoelectric/electrostrictive devicewhich is provided with a movable section to be operated on the basis ofa displacement action of a piezoelectric/electrostrictive element, or apiezoelectric/electrostrictive device which is capable of detectingdisplacement of a movable section by the aid of apiezoelectric/electrostrictive element, and a method for producing thesame. In particular, the present invention relates to apiezoelectric/electrostrictive device which is excellent in strength,shock resistance, and moisture resistance and which makes it possible toefficiently operate a movable section to a great extent, and a methodfor producing the same.

BACKGROUND OF THE INVENTION

Recently, a displacement element, which makes it possible to adjust theoptical path length and the position in an order of submicron, isrequired, for example, in the fields of optics, magnetic recording, andprecision machining. Development is advanced for the displacementelement based on the use of the displacement brought about by theinverse piezoelectric effect or the electrostrictive effect caused whena voltage is applied to a piezoelectric/electrostrictive material (forexample, a ferroelectric material).

As shown in FIG. 53, for example, those hitherto disclosed as such adisplacement element include a piezoelectric actuator comprising afixation section 404, a movable section 406, and a beam section 408 forsupporting them which are formed in an integrated manner with a hole 402provided through a plate-shaped member 400 composed of apiezoelectric/electrostrictive material and with an electrode layer 410provided on the beam section 408 (see, for example, Japanese Laid-OpenPatent Publication No. 10-136665).

The piezoelectric actuator is operated such that when a voltage isapplied to the electrode layer 410, the beam section 408 makes expansionand contraction in a direction along a line obtained by connecting thefixation section 404 and the movable section 406 in accordance with theinverse piezoelectric effect or the electrostrictive effect. Therefore,the movable section 406 can perform circular arc-shaped displacement orrotational displacement in the plane of the plate-shaped member 400.

On the other hand, Japanese Laid-Open Patent Publication No. 63-64640discloses a technique in relation to an actuator based on the use of abimorph. In this technique, electrodes for the bimorph are provided in adivided manner. The actuator is driven in accordance with the selectionof the divided electrodes, and thus the highly accurate positioning isperformed at a high speed. This document (especially in FIG. 4)discloses a structure in which, for example, two bimorphs are used in anopposed manner.

However, the piezoelectric actuator described above involves such aproblem that the amount of operation of the movable section 406 issmall, because the displacement in the direction of expansion andcontraction of the piezoelectric/electrostrictive material (i.e., in thein-plane direction of the plate-shaped member 400) is transmitted to themovable section 406 as it is.

All of the parts of the piezoelectric actuator are made of thepiezoelectric/electrostrictive material which is a fragile materialhaving a relatively heavy weight. Therefore, the following problemsarise. That is, the mechanical strength is low, and the piezoelectricactuator is inferior in handling performance, shock resistance, andmoisture resistance. Further, the piezoelectric actuator itself isheavy, and its operation tends to be affected by harmful vibrations (forexample, residual vibration and noise vibration during high speedoperation).

In order to solve the problems described above, it has been suggestedthat the hole 402 is filled with a filler material having flexibility.However, it is clear that the amount of displacement, which is broughtabout by the inverse piezoelectric effect or the electrostrictiveeffect, is decreased even when the filler material is merely used.

SUMMARY OF THE INVENTION

The present invention has been made taking the foregoing problems intoconsideration, an object of which is to provide apiezoelectric/electrostrictive device and a method for producing thesame which make it possible to obtain a displacement element that isscarcely affected by harmful vibration and capable of high speedresponse with high mechanical strength while being excellent in handlingperformance, shock resistance, and moisture resistance, making itpossible to realize a long service life of a device, and improve thehandling performance of the device and the attachment performance forparts to be attached to the movable section or the fixation performanceof the device, so that the movable section may be greatly displaced at arelatively low voltage, and it is possible to achieve a high speed ofthe displacement action of the device, especially of the movable section(realization of a high resonance frequency), as well as a sensor elementwhich makes it possible to accurately detect vibration of the movablesection.

According to the present invention, there is provided apiezoelectric/electrostrictive device comprising a pair of mutuallyopposing thin plate sections made of metal and a fixation sectionsecured to the thin plate sections by the aid of an adhesive; a movablesection provided at forward end portions of the pair of thin platesections; and one or more piezoelectric/electrostrictive elementsarranged on at least one thin plate section of the pair of thin platesections; wherein any one of the movable section and the fixationsection has mutually opposing end surfaces; and a distance between theend surfaces is not less than a length of the movable section.

The device is excellent in strength and toughness, and the device iscapable of responding to any quick displacement action, because the thinplate section is made of metal. That is, according to the presentinvention, it is possible to sufficiently respond to any variation ofthe environment of the use and any severe state of the use. The deviceis excellent in shock resistance. It is possible to realize a longservice life of the piezoelectric/electrostrictive device, and it ispossible to improve the handling performance of thepiezoelectric/electrostrictive device. Further, the thin plate sectioncan be greatly displaced at a relatively low voltage, and it is possibleto achieve the realization of a high speed of the displacement action ofthe thin plate section (realize a high resonance frequency), because thethin plate section has high rigidity, and the actuator film has a thickfilm thickness and high rigidity.

It is also preferable that the piezoelectric/electrostrictive elementhas a film-shaped configuration, and it is secured to the thin platesection by the aid of an adhesive. It is also preferable that thepiezoelectric/electrostrictive element is constructed to have apiezoelectric/electrostrictive layer and a pair of electrodes formed onthe piezoelectric/electrostrictive layer. In this arrangement, thevibration, which is caused by the piezoelectric/electrostrictiveelement, can be efficiently transmitted via the thin plate section tothe movable section or the fixation section. It is possible to improvethe response performance.

Especially, it is preferable that the piezoelectric/electrostrictiveelement is constructed in a stacked form comprising a plurality of unitseach including the piezoelectric/electrostrictive layer and the pair ofelectrodes. When the arrangement as described above is adopted, thefollowing feature is achieved. That is, the generated force of thepiezoelectric/electrostrictive element is increased, and thus it ispossible to obtain large displacement. Further, it is possible to obtaina high resonance frequency owing to the increase in rigidity of thedevice itself, making it easy to achieve the high speed of thedisplacement action.

Those usable for the adhesive include organic resin, glass, brazingmaterial, and solder.

Any one of the movable section and the fixation section may be providedwith a cutoff section; and a part of the cutoff section constitutes themutually opposing end surfaces. In this arrangement, a gap may be formedbetween the mutually opposing end surfaces. It is also preferable that amember which is the same as a constitutive member of any one of themovable section and the fixation section, or a plurality of memberswhich are different therefrom are interposed between the mutuallyopposing end surfaces, the same member or the different membersincluding, for example, glass, cement, and organic resin, preferablyorganic resin such as those based on epoxy, acrylic, polyimide, phenol,silicone, terpene, xylene, styrene, melamine, methacrylic, and rubber,or mixture or copolymer thereof. Especially, in view of, for example,the joining performance, the handling performance, and the hardness, itis preferable to allow organic resin or the like based on epoxy,acrylic, and methacrylic to intervene. In order to further enhance thehardness, it is also preferable to mix a filler such as an inorganicmaterial.

Especially, it is possible to effectively realize a light weight of themovable section or the fixation section by forming the gap between themutually opposing end surfaces, allowing the member lighter than theconstitutive member of the movable section or the fixation section tointervene between the mutually opposing end surfaces, or joining the endsurfaces with small one of the members described above. Accordingly, itis possible to increase the resonance frequency without decreasing theamount of displacement of the movable section or the fixation section.

When the gap is formed between the mutually opposing end surfaces, apart of the movable section or the fixation section including one endsurface and another part of the movable section or the fixation sectionincluding the other end surface are more flexible, resulting in strongresistance to the deformation. Therefore, it is possible to obtainexcellent handling performance of the piezoelectric/electrostrictivedevice.

Further, the distance between the end surfaces is not less than thelength of the movable section. Therefore, when another part is attachedto the movable section, it is easy to suppress the influence of thedimensional accuracy, even when the dimensional accuracy of the endsurface or the part is low. Thus, it is possible to improve theattachment performance for the part. It is now assumed that the part issecured, for example, with an adhesive or the like. The part can be heldby being interposed between the end surfaces and being attached on bothsides. Thus, it is possible to reliably secure the part.

When the part is held by being interposed on both sides, the height ofthe part and the height of the movable section are not simply added.Accordingly, it is possible to maintain the height of the wholeincluding the part to be low. Further, the length of the movable sectioncan be made smaller than the distance on the side of the end surface.Therefore, the physical property of an adhesive or the like for stickingor bonding the part effectively makes the action. Thus, it is possibleto increase the displacement.

On the other hand, when the fixation section has the mutually opposingend surfaces, it is possible to strongly fix thepiezoelectric/electrostrictive device according to this invention to apredetermined fixation portion. Thus, it is possible to improve thereliability.

As described above, according to the present invention, it is possibleto realize a light weight of the device, especially a light weight ofthe movable section or the fixation section.

In the production of the piezoelectric/electrostrictive device, forexample, when the piezoelectric/electrostrictive element is secured tothe thin plate section made of metal by the aid of the adhesive,especially at the solidification stage of the adhesive, the internalresidual stress is generated at a portion to be formed into thepiezoelectric/electrostrictive element and/or the thin plate section.

If the piezoelectric/electrostrictive device is manufactured and usedstarting from this state, the movable section does not exhibit thedesired displacement in some cases, even when a predetermined electricfield is applied to the piezoelectric/electrostrictive layer forconstructing the piezoelectric/electrostrictive element, because of thefollowing reason. That is, the material characteristic of thepiezoelectric/electrostrictive layer and the displacement action of themovable section are inhibited by the internal residual stress generatedin the piezoelectric/electrostrictive element and/or the thin platesection.

In the present invention, the mutually opposing end surfaces areprovided on any one of the movable section and the fixation section.Therefore, the distance between the end surfaces is, for example,shortened by the internal residual stress generated in thepiezoelectric/electrostrictive element and/or the thin plate section.That is, the internal residual stress, which has been generated in thepiezoelectric/electrostrictive element and/or the thin plate section, isreleased by the movement of the end surfaces.

Further, in the present invention, the distance between the end surfacesis made to be wide. Therefore, even when the distance between the endsurfaces is narrowed due to the internal residual stress, it is possibleto give a margin sufficient to attach another part between the endsurfaces.

As described above, in the present invention, the displacement action ofthe movable section is not inhibited by the internal residual stress. Itis possible to obtain the displacement action of the movable section asapproximately designed and expected. Additionally, the release of theinternal residual stress also makes it possible to improve themechanical strength of the device.

When a hole is formed by both inner walls of the pair of thin platesections, an inner wall of the movable section, inner walls of theplurality of members, and an inner wall of the fixation section, it isalso preferable that the hole is filled with a gel material. In thisarrangement, although the displacement action of the movable section isusually restricted due to the presence of the filler material, theinvention described above intends to reduce the weight as a result ofthe formation of the end surfaces on the movable section or the fixationsection, and increase the displacement amount of the movable section.Therefore, the restriction of the displacement action of the movablesection by the filler material is counteracted, and it is possible torealize the effect owing to the presence of the filler material, i.e.,the realization of the high resonance frequency and the ensuring of therigidity.

In the present invention, when the plurality of members as describedabove are allowed to intervene between the end surfaces, at least onemember of the plurality of members may be organic resin.

According to another aspect of the present invention, there is provideda method for producing a piezoelectric/electrostrictive devicecomprising a pair of mutually opposing thin plate sections made of metaland a fixation section secured to the thin plate sections by the aid ofan adhesive; a movable section provided at forward end portions of thepair of thin plate sections; and one or morepiezoelectric/electrostrictive elements arranged on at least one thinplate section of the pair of thin plate sections; the method comprisinga first step of manufacturing a second substrate by securing, to a firstsubstrate, metal plates to be formed into the thin plate sectionsthereafter; and a second step of forming the movable section or thefixation section having mutually opposing end surfaces wherein adistance between the end surfaces is not less than a length of themovable section, by means of at least one time of cutoff treatment forthe second substrate.

Accordingly, there is provided the movable section or the fixationsection which has the mutually opposing end surfaces. Therefore, theinternal residual stress, which has been generated in thepiezoelectric/electrostrictive element and/or the thin plate sectionduring the production, is released, for example, by shortening thedistance between the end surfaces. As a result, the displacement actionof the movable section is not inhibited by the internal residual stress.Especially, the device is excellent in strength and toughness, and itcan respond to any quick displacement action, because the metal is usedfor the thin plate section.

The provision of the movable section or the fixation section having themutually opposing end surfaces realizes the light weight of the movablesection or the fixation section. Therefore, thepiezoelectric/electrostrictive device, which makes it possible toincrease the resonance frequency, can be efficiently produced with easewithout decreasing the amount of displacement of the movable section.Thus, it is possible to realize the mass production of the highperformance piezoelectric/electrostrictive device.

Further, the movable section or the fixation section is bent moreflexibly, and it is strongly resistant to deformation. Therefore, thepiezoelectric/electrostrictive device is excellent in handlingperformance. Owing to the presence of the mutually opposing end surfacesand the wide distance between the end surfaces, when another part isattached to the movable section, it is easy to suppress the influence ofthe dimensional accuracy, even when the dimensional accuracy of the endsurface or the part is low. Thus, it is possible to improve theattachment performance for the part. When a part is interposed andbonded, it is possible to improve the displacement.

The production method described above may further comprise a step ofsecuring the piezoelectric/electrostrictive element to an outer surfaceof the metal plate to be formed into the thin plate section thereafter,by the aid of an adhesive. Accordingly, in the production of thepiezoelectric/electrostrictive device, especially when thepiezoelectric/electrostrictive element is secured to the thin platesection made of metal by the aid of the adhesive, especially at thesolidification stage of the adhesive, the internal residual stress,which is generated in the piezoelectric/electrostrictive element and/orthe thin plate section, can be effectively released. Therefore, when thepiezoelectric/electrostrictive device is produced, it is possible torealize the light weight of the device, especially the light weight ofthe movable section or the fixation section, and improve the handlingperformance of the device, the attachment performance for parts to beattached to the movable section, and the fixation performance of thedevice. Thus, it is possible to allow the movable section to make largedisplacement.

The piezoelectric/electrostrictive element may be previously secured tothe outer surface of the metal plate, before the metal plate to beformed into the thin plate section thereafter is secured to the firstsubstrate.

When the first substrate is composed of a ceramic laminate, the methodmay further comprise a ceramic laminate-manufacturing step of laminatingand sintering one or more ceramic green sheets each having at least awindow to manufacture a ceramic laminate; and a hybridlaminate-manufacturing step of securing, to the ceramic laminate, themetal plate to be formed into the thin plate section thereafter by theaid of the adhesive to manufacture a hybrid laminate.

In this process, it is also preferable that in the ceramiclaminate-manufacturing step, a plurality of ceramic green sheets, whichhave windows for forming the movable section or the fixation sectionhaving at least the mutually opposing end surfaces, are sintered tomanufacture the ceramic laminate.

When the first substrate is composed of metal, the method may furthercomprise a step of laminating one or more metal sheets each having atleast a window to manufacture the first substrate, or the firstsubstrate may be composed of a bulk metal member.

The method may further comprise a step of allowing a plurality ofmembers different from a constitutive member of the movable section orthe fixation section to intervene between the mutually opposing endsurfaces. In this case, organic resin may be used as at least one memberof the plurality of members.

It is possible to use, as the adhesive, an adhesive composed of organicresin, or an adhesive composed of glass, brazing material, or solder.

Therefore, the piezoelectric/electrostrictive device and the method forproducing the same according to the present invention can make the useof the active device including, for example, various transducers,various actuators, frequency region functional parts (filters),transformers, vibrators, resonators, oscillators, and discriminators forthe communication and the power generation, as well as the sensorelement for various sensors including, for example, ultrasonic sensors,acceleration sensors, angular velocity sensors, shock sensors, and masssensors. Especially, the piezoelectric/electrostrictive device and themethod for producing the same according to the present invention can bepreferably utilized for various actuators to be used for the mechanismfor adjusting the displacement and the positioning and for adjusting theangle for various precision parts such as those of optical instrumentsand precision mechanical equipments.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which a preferredembodiment of the present invention is shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a first embodiment;

FIG. 2 shows a perspective view illustrating a first modified embodimentof the piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 3 shows a perspective view illustrating a second modifiedembodiment of the piezoelectric/electrostrictive device according to thefirst embodiment;

FIG. 4 shows a perspective view illustrating a third modified embodimentof the piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 5 shows a perspective view illustrating a fourth modifiedembodiment of the piezoelectric/electrostrictive device according to thefirst embodiment;

FIG. 6 shows a perspective view illustrating a fifth modified embodimentof the piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 7 shows a perspective view illustrating another embodiment of thepiezoelectric/electrostrictive device concerning the fifth modifiedembodiment;

FIG. 8 shows a perspective view illustrating a sixth modified embodimentof the piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 9 shows a perspective view illustrating a seventh modifiedembodiment of the piezoelectric/electrostrictive device according to thefirst embodiment;

FIG. 10 shows, with partial omission, another embodiment of thepiezoelectric/electrostrictive element;

FIG. 11 shows, with partial omission, still another embodiment of thepiezoelectric/electrostrictive element;

FIG. 12 illustrates a situation in which both of thepiezoelectric/electrostrictive elements do not make the displacementaction in the piezoelectric/electrostrictive device according to thefirst embodiment;

FIG. 13A shows a waveform illustrating a voltage waveform to be appliedto the first piezoelectric/electrostrictive element;

FIG. 13B shows a waveform illustrating a voltage waveform to be appliedto the second piezoelectric/electrostrictive element;

FIG. 14 illustrates a situation in which thepiezoelectric/electrostrictive element makes the displacement action inthe piezoelectric/electrostrictive device according to the firstembodiment;

FIG. 15 shows a perspective view illustrating an arrangement in which asecond piezoelectric/electrostrictive device is secured to a movablesection of a first piezoelectric/electrostrictive device;

FIG. 16A illustrates a process for laminating necessary ceramic greensheets in a first production method;

FIG. 16B illustrates a state in which a ceramic green laminate isformed;

FIG. 17A illustrates a state in which the ceramic green laminate issintered to provide a ceramic laminate;

FIG. 17B illustrates a state in which piezoelectric/electrostrictiveelements, which are constructed as separate members, are bonded to thesurfaces of metal plates to serve as thin plate sections respectively;

FIG. 18 illustrates a state in the first production method in which themetal plate is bonded to the ceramic laminate to provide a hybridlaminate;

FIG. 19 illustrates a state in which the hybrid laminate is cut alongpredetermined cutting lines to manufacture thepiezoelectric/electrostrictive device according to the first embodiment;

FIG. 20A illustrates a process for laminating necessary ceramic greensheets in a second production method;

FIG. 20B illustrates a state in which a ceramic green laminate isformed;

FIG. 21A illustrates a state in which the ceramic green laminate issintered to provide a ceramic laminate, and then a hole is filled with afiller material;

FIG. 21B illustrates a state in which metal plates to serve as thinplate sections respectively are bonded to the ceramic laminate toprovide a hybrid laminate;

FIG. 22 illustrates a state in which piezoelectric/electrostrictiveelements, which are constructed as separate members, are bonded to thesurfaces of the metal plates of the hybrid laminate;

FIG. 23 illustrates a state in which the piezoelectric/electrostrictivedevice according to the first embodiment is manufactured by cutting thehybrid laminate along predetermined cutting lines;

FIG. 24 shows a perspective view illustrating an arrangement of apiezoelectric/electrostrictive device according to a second embodiment;

FIG. 25 shows a perspective view illustrating another arrangement of thepiezoelectric/electrostrictive device according to the secondembodiment;

FIG. 26 shows a magnified view illustrating an exemplary arrangement ofa stacked type piezoelectric/electrostrictive element;

FIG. 27 shows a magnified view illustrating a preferred exemplaryarrangement of the stacked type piezoelectric/electrostrictive elementshown in FIG. 26;

FIG. 28 shows a magnified view illustrating another exemplaryarrangement of a stacked type piezoelectric/electrostrictive element;

FIG. 29 shows a magnified view illustrating a preferred exemplaryarrangement of the stacked type piezoelectric/electrostrictive elementshown in FIG. 28;

FIG. 30 shows a perspective view illustrating still another arrangementof the piezoelectric/electrostrictive device according to the secondembodiment;

FIG. 31 illustrates the preferred dimensional relationship concerningthe piezoelectric/electrostrictive device according to the secondembodiment;

FIG. 32 illustrates a state in a third production method in which arectangular hole is bored through a central portion of a stainless steelplate to manufacture a substrate having a rectangular annular structure;

FIG. 33 illustrates a state in which an adhesive is formed on the firststainless steel thin plate;

FIG. 34 illustrates a state in which the stacked typepiezoelectric/electrostrictive element is bonded to the first stainlesssteel thin plate with the adhesive intervening therebetween;

FIG. 35 illustrates a state in which the first and second stainlesssteel thin plates are bonded to the substrate by the aid of theadhesive;

FIG. 36 illustrates a state in which a manufactured master device blockis cut;

FIG. 37 illustrates a state in a fourth production method in which arectangular hole is bored through a central portion of a stainless steelplate to manufacture a substrate having a rectangular annular structure,and first and second stainless steel thin plates are bonded to thesubstrate by the aid of an adhesive;

FIG. 38 illustrates a state in which the first and second stainlesssteel thin plates are bonded by the aid of the adhesive;

FIG. 39 illustrates a state in which the adhesive is formed on the firststainless steel thin plate;

FIG. 40 illustrates a state in which a stacked typepiezoelectric/electrostrictive element is bonded to the first stainlesssteel thin plate by the aid of the adhesive;

FIG. 41 illustrates a state in which first and second stainless steelthin plates are bonded to another exemplary substrate by the aid of anadhesive;

FIG. 42 illustrates an example in a fifth production method in whichbumps are provided at portions of respective thin plate sections towhich at least a fixation section is bonded;

FIG. 43 illustrates an example in the fifth production method in whichbumps are not provided at portions of respective thin plate sections towhich at least a fixation section is bonded;

FIG. 44 illustrates an example in the fifth production method in whichno bump is provided on respective thin plate sections;

FIG. 45 illustrates an example in the fifth production method in whichprojections for forming compartments for adhesion are provided atportions of respective thin plate sections to which a fixation sectionis bonded;

FIG. 46 illustrates an example in the fifth production method in which alarge fixation section is used;

FIG. 47 illustrates a first technique (to define holes through a thinplate section);

FIG. 48 illustrates a second technique (to roughen the surfaces of athin plate section and a piezoelectric/electrostrictive element);

FIG. 49 illustrates a third technique (to provide a curvature forstick-out portions of an adhesive);

FIG. 50 illustrates a fourth technique (to chamfer angular portions of afixation section);

FIG. 51 illustrates a fifth technique (to direct burrs outwardly);

FIG. 52 illustrates a sixth technique (to change the thickness for thinplate sections); and

FIG. 53 shows an arrangement of a piezoelectric/electrostrictive deviceconcerning an illustrative conventional technique.

DETAILED DESCRIPTION OF THE INVENTION

Explanation will be made below with reference to FIGS. 1 to 52 forillustrative embodiments of the piezoelectric/electrostrictive deviceand the production method for the same according to the presentinvention.

It is noted that the piezoelectric/electrostrictive device resides in aconcept which includes the element for mutually converting the electricenergy and the mechanical energy by the aid of thepiezoelectric/electrostrictive element. Therefore, thepiezoelectric/electrostrictive device is most preferably used as theactive element such as various actuators and vibrators, especially asthe displacement element based on the use of the displacement broughtabout by the inverse piezoelectric effect or the electrostrictiveeffect. Additionally, the piezoelectric/electrostrictive device is alsopreferably used as the passive element such as acceleration sensorelements and shock sensor elements.

As shown in FIG. 1, the piezoelectric/electrostrictive device 10Aaccording to the first embodiment has a substrate 14 which has a lengthyrectangular parallelepiped-shaped configuration as a whole and which hasa hole 12 provided at an approximately central portion in the major axisdirection thereof.

The substrate 14 comprises a pair of mutually opposing thin platesections 16 a, 16 b, a movable section 20, and a fixation section 22 forsupporting the pair of thin plate sections 16 a, 16 b and the movablesection 20. Piezoelectric/electrostrictive elements 24 a, 24 b areformed at respective parts of at least the thin plate sections 16 a, 16b respectively.

The substrate 14 may be constructed by using ceramics or metal for theentire substrate 14. Alternatively, the substrate 14 may have a hybridstructure obtained by combining those produced with ceramic and metalmaterials. Further, those adoptable for constructing the substrate 14include, for example, a structure in which respective parts are bondedto one another with an adhesive such as organic resin and glass, and ametal integrated structure which is integrated into one unit, forexample, by means of brazing, soldering, eutectic bonding, or welding.

In the first embodiment, the substrate 14 has a hybrid structure inwhich the pair of thin plate sections 16 a, 16 b are made of metal, andthe other parts, i.e., the movable section 20 and the fixation section22 are made of ceramics. Specifically, the thin plate sections 16 a, 16b made of metal are secured by an adhesive 200 to respective sidesurfaces of the movable section 20 and the fixation section 22 made ofceramics. It is a matter of course that all of the thin plate sections16 a, 16 b, the movable section 20, and the fixation section 22 may bemade of metal.

The piezoelectric/electrostrictive elements 24 a, 24 b are prepared asseparate members as described later on, and the preparedpiezoelectric/electrostrictive elements 24 a, 24 b are affixed to thesubstrate 14 with an adhesive such as organic resin or glass or by meansof brazing, soldering, or eutectic bonding. Alternatively, thepiezoelectric/electrostrictive elements 24 a, 24 b are directly formedon the substrate 14 by using the film formation method not by using theadhesive method described above. In the first embodiment, thepiezoelectric/electrostrictive elements 24 a, 24 b are secured onto thethin plate sections 16 a, 16 b by the aid of an adhesive 202respectively.

The piezoelectric/electrostrictive device 10A includes the hole 12having, for example, a rectangular configuration which is formed by bothinner walls of the pair of thin plate sections 16 a, 16 b, an inner wall20 a of the movable section 20, and an inner wall 22 a of the fixationsection 22. The piezoelectric/electrostrictive device 10A is constructedsuch that the movable section 20 is displaced in accordance with thedriving of the piezoelectric/electrostrictive element or elements 24 aand/or 24 b, or the displacement of the movable section 20 is detectedby the piezoelectric/electrostrictive element or elements 24 a and/or 24b.

Each of the piezoelectric/electrostrictive elements 24 a, 24 b comprisesa piezoelectric/electrostrictive layer 26, and a pair of electrodes 28,30 formed on both sides of the piezoelectric/electrostrictive layer 26.One electrode 28 of the pair of electrodes 28, 30 is formed at least oneach of the pair of thin plate sections 16 a, 16 b.

In the embodiment shown in FIG. 1, respective forward end surfaces ofthe pair of electrodes 28, 30 and the piezoelectric/electrostrictivelayer 26 for constructing the piezoelectric/electrostrictive element 24a, 24 b are substantially aligned. A substantial driving portion 18 ofthe piezoelectric/electrostrictive element 24 a, 24 b (portion at whichthe pair of electrodes 28, 30 are overlapped with each other with thepiezoelectric/electrostrictive layer 26 interposed therebetween) iscontinuously formed over a range from a part of the outer surface of thefixation section 22 to a part of the outer surface of the thin platesection 16 a, 16 b. Especially, in this embodiment, the respectiveforward end surfaces of the pair of electrodes 28, 30 are located at thepositions slightly deviated toward rearward ends from the inner wall 20a of the movable section 20. Of course, thepiezoelectric/electrostrictive element 24 a, 24 b may be formed suchthat the substantial driving portion 18 is located over a range from apart of the movable section 20 to a part of the thin plate section 16 a,16 b.

As shown in FIG. 1, the piezoelectric/electrostrictive device 10Aaccording to the first embodiment described above includes mutuallyopposing end surfaces 36 a, 36 b which are formed in the movable section20. Each of the end surfaces 36 a, 36 b is a surface substantiallyparallel to the side surface of the movable section 20, i.e., thesurface for forming the element. The respective end surfaces 36 a, 36 bare separated from each other from the upper surface of the movablesection 20 to the hole 12. In this arrangement, as shown in FIG. 12, forexample, it is preferable that the distances Da, Db, which range fromthe central axis n of the movable section 20 to the respective endsurfaces 36 a, 36 b, are substantially equal to one another.

As shown in FIG. 1, for example, a gap (air) 38 may be allowed tointervene between the end surfaces 36 a, 36 b. Alternatively, as in apiezoelectric/electrostrictive device 10Ag according to a seventhmodified embodiment shown in FIG. 9 or as shown in FIG. 12, a memberdifferent from the constitutive member of the movable section 20, forexample, a member 40 composed of, for example, resin or the like may beallowed to intervene between the end surfaces 36 a, 36 b.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the voltage is applied to the pair of electrodes 28, 30 viaterminals (pads) 32, 34 of the respective electrodes 28, 30 formed onthe both side surfaces (element formation surfaces) of the fixationsection 22 respectively. The respective terminals 32, 34 are positionedas follows. That is, the terminal 32 corresponding to the firstelectrode 28 is formed at the position deviated toward the rearward endof the fixation section 22. The terminal 34 corresponding to the secondelectrode 30 disposed on the side of the external space is formed at theposition deviated toward the inner wall 22 a of the fixation section 22.

In this embodiment, the piezoelectric/electrostrictive device 10A can beindividually fixed by utilizing the surfaces respectively different fromthe surfaces on which the terminals 32, 34 are arranged. As a result, itis possible to obtain the high reliability for both of the fixation ofthe piezoelectric/electrostrictive device 10A and the electricconnection between the circuit and the terminals 32, 34. In thisarrangement, the electric connection between the terminals 32, 34 andthe circuit is made, for example, by means of the flexible printedcircuit (also referred to as FPC), the flexible flat cable (alsoreferred to as FFC), and the wire bonding.

Structures other than the structure shown in FIG. 1 are available toconstruct the piezoelectric/electrostrictive element 24 a, 24 b. Thatis, as in a piezoelectric/electrostrictive device 10Aa according to afirst modified embodiment shown in FIG. 2, it is also preferable thatthe respective forward ends of the pair of electrodes 28, 30 forconstructing the piezoelectric/electrostrictive element 24 a, 24 b arealigned, and only the forward end of the piezoelectric/electrostrictivelayer 26 is allowed to protrude toward the movable section 20.Alternatively, as in a piezoelectric/electrostrictive device 10Abaccording to a second modified embodiment shown in FIG. 3, it is alsopreferable that the respective forward ends of the first electrode 28and the piezoelectric/electrostrictive layer 26 are aligned, and onlythe forward end of the second electrode 30 is disposed at a positiondeviated toward the fixation section 22. Thepiezoelectric/electrostrictive device 10Ab shown in FIG. 3 isillustrative of the case in which mutually opposing end surfaces 36 a,36 b are provided in the fixation section 22 in place of the movablesection 20.

Alternatively, as in a piezoelectric/electrostrictive device 10Acaccording to a third modified embodiment shown in FIG. 4, it is alsopreferable that the respective forward ends of the first electrode 28and the piezoelectric/electrostrictive layer 26 are allowed to extend upto the side surface of the movable section 20, and the forward end ofthe second electrode 30 is located at an approximately central portionin the length direction (Z axis direction) of the thin plate section 16a, 16 b.

In the embodiments described above, the piezoelectric/electrostrictiveelement 24 a, 24 b is constructed by the piezoelectric/electrostrictivelayer 26 having the one-layered structure and the pair of electrodes 28,30. Alternatively, it is also preferable that thepiezoelectric/electrostrictive element 24 a, 24 b is constructed in astacked form composed of a plurality of units each comprising thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30.

For example, as in a piezoelectric/electrostrictive device 10Adaccording to a fourth modified embodiment shown in FIG. 5, each of thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 resides in a multilayered structure. The first electrodes 28 and thesecond electrodes 30 are alternately stacked with each other to providethe piezoelectric/electrostrictive element 24 a, 24 b which has amultiple stage structure at a portion (substantial driving portion 18)at which the first electrodes 28 and the second electrodes 30 areoverlapped with each other with the piezoelectric/electrostrictive layer26 interposed therebetween. FIG. 5 is illustrative of the followingcase. That is, the piezoelectric/electrostrictive layer 26 has thethree-layered structure. The first electrodes 28 are formed in aseparate manner respectively on the lower surface of the first layer(side surface of the thin plate section 16 a, 16 b) and on the uppersurface of the second layer. The second electrodes 30 are formed in aseparate manner respectively on the upper surface of the first layer andon the upper surface of the third layer. Further, terminals 32 a, 32 bare provided on respective ends of the first electrodes 28 respectively,and terminals 34 a, 34 b are provided on respective ends of the secondelectrodes 30 respectively.

As in a piezoelectric/electrostrictive device 10Ae according to a fifthmodified embodiment shown in FIG. 6, each of thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 resides in a multilayered structure. The first electrode 28 and thesecond electrode 30 are alternately stacked with each other so that asubstantially comb-shaped configuration is obtained in cross section toprovide the piezoelectric/electrostrictive element 24 a, 24 b which hasa multiple stage structure at a portion (substantial driving portion 18)at which the first electrode 28 and the second electrode 30 areoverlapped with each other with the piezoelectric/electrostrictive layer26 interposed therebetween. FIG. 6 is illustrative of the followingcase. That is, the piezoelectric/electrostrictive layer 26 has thethree-layered structure. The first electrode 28 is formed in acomb-shaped configuration to be located on the lower surface of thefirst layer (side surface of the thin plate section 16 a, 16 b) and onthe upper surface of the second layer. The second electrode 30 is formedin a comb-shaped configuration to be located on the upper surface of thefirst layer and on the upper surface of the third layer. In the case ofthis structure, each of the first electrode 28 and the second electrode30 is continuous and common. Accordingly, it is possible to decrease thenumber of terminals 32, 34 as compared with the structure shown in FIG.5. Therefore, it is possible to suppress the increase in size whichwould be otherwise involved in the multilayered structure of thepiezoelectric/electrostrictive element 24 a, 24 b.

Another example of the piezoelectric/electrostrictive device 10Aeaccording to the fifth modified embodiment is shown in FIG. 7. In thiscase, it is also preferable to form the piezoelectric/electrostrictiveelement 24 a, 24 b so that the forward end thereof stays on the thinplate section 16 a, 16 b. FIG. 7 is illustrative of the case in whichthe forward end of the piezoelectric/electrostrictive element 24 a, 24 bis located at a substantially central portion in the length direction ofthe thin plate section. This arrangement is advantageous in that themovable section 20 can be displaced to a great extent.

Alternatively, as in a piezoelectric/electrostrictive device 10Afaccording to a sixth modified embodiment shown in FIG. 8, it is alsopreferable that two piezoelectric/electrostrictive elements 24 a 1, 24 b1 having the multiple stage structure are formed to extend over thefixation section 22 and the thin plate section 16 a, 16 b respectively,and another two piezoelectric/electrostrictive elements 24 a 2, 24 b 2having the multiple stage structure are formed to extend over themovable section 20 and the thin plate section 16 a, 16 b respectively.In this arrangement, the movable section 20 can be displaced extremelygreatly owing to the effect that the piezoelectric/electrostrictiveelement 24 a, 24 b has the multiple stage structure and the effect thatthe number of points of action to displace the movable section 20 isincreased. Further, the piezoelectric/electrostrictive device 10Af isexcellent in high speed response performance, which is preferred.

Alternatively, as in a piezoelectric/electrostrictive device 10Agaccording to a seventh modified embodiment shown in FIG. 9, it is alsopreferable that the piezoelectric/electrostrictive layer 26 has thetwo-layered structure to provide the piezoelectric/electrostrictiveelement 24 a, 24 b having the multiple stage structure which is formedsuch that the first electrode 28 is formed to have a comb-shapedconfiguration to be located on the lower surface of the first layer(side surface of the thin plate section 16 a, 16 b) and on the uppersurface of the second layer, and the second electrode 30 is located onthe upper surface of the first layer. In this embodiment, the spacebetween the end surfaces 36 a, 36 b of the movable section 20 is filledwith a member which is different from the movable section 20.

The multiple stage structure of the piezoelectric/electrostrictiveelement 24 a, 24 b as described above increases the force generated bythe piezoelectric/electrostrictive element 24 a, 24 b, and thus it ispossible to obtain the large displacement. Further, the rigidity of thepiezoelectric/electrostrictive device 10A itself is increased, and thusit is possible to realize the high resonance frequency. It is possibleto achieve the high speed displacement action with ease.

When the number of stages is increased, it is possible to increase thedriving force. However, the electric power consumption is also increasedin accordance therewith. Therefore, when the device is practicallyproduced and used, for example, it is preferable that the number ofstages is appropriately determined depending on the way of use and thestate of use. In the case of the piezoelectric/electrostrictive device10A according to the first embodiment, even when the driving force isincreased by providing the multiple stage structure of thepiezoelectric/electrostrictive element 24 a, 24 b, the width of the thinplate section 16 a, 16 b (distance in the Y axis direction) is basicallyunchanged. Therefore, the device is extremely preferred to makeapplication, for example, to the actuator for the purpose of the ringingcontrol and the positioning of the magnetic head for the hard disk to beused in an extremely narrow gap. Further, when the device is used as asensor (for example, an acceleration sensor), the device provides thefollowing advantage, because the electrostatic capacity is increased,and the generated electric charge is increased, owing to the multiplestage structure. That is, the level of the electric signal generated bythe sensor is increased, and it is easy to perform the processing in asignal processing circuit to be connected to the subsequent stage of thesensor.

The piezoelectric/electrostrictive element 24 a, 24 b described above isillustrative of the case of the so-called sandwich structure in whichthe piezoelectric/electrostrictive layer 26 is interposed between thepair of electrodes 28, 30. Alternatively, as shown in FIG. 10, a pair ofcomb-shaped electrodes 28, 30 may be formed on the first principalsurface of the piezoelectric/electrostrictive layer 26 formed on atleast the side surface of the thin plate section 16 a, 16 b. Furtheralternatively, as shown in FIG. 11, a pair of comb-shaped electrodes 28,30 are formed and embedded in the piezoelectric/electrostrictive layer26 formed on at least the side surface of the thin plate section 16 a,16 b.

The structure shown in FIG. 10 is advantageous in that it is possible tosuppress the electric power consumption to be low. The structure shownin FIG. 11 makes it possible to effectively utilize the inversepiezoelectric effect in the direction of the electric field having largegenerated force and strain, which is advantageous to cause the largedisplacement.

Specifically, the piezoelectric/electrostrictive element 24 a, 24 bshown in FIG. 10 comprises the pair of electrodes 28, 30 having thecomb-shaped structure formed on the first principal surface of thepiezoelectric/electrostrictive layer 26. In this structure, the firstelectrode 28 and the second electrode 30 are mutually opposed to oneanother in an alternate manner with a gap 29 having a constant widthinterposed therebetween. FIG. 10 is illustrative of the case in whichthe pair of electrodes 28, 30 are formed on the first principal surfaceof the piezoelectric/electrostrictive layer 26. Alternatively, the pairof electrodes 28, 30 may be formed between the thin plate section 16 a,16 b and the piezoelectric/electrostrictive layer 26. Furtheralternatively, the pair of comb-shaped electrodes 28, 30 may be formedon the first principal surface of the piezoelectric/electrostrictivelayer 26 and between the thin plate section 16 a, 16 b and thepiezoelectric/electrostrictive layer 26 respectively.

On the other hand, in the piezoelectric/electrostrictive element 24 a,24 b shown in FIG. 11, the pair of electrodes 28, 30 having thecomb-shaped structure are formed so that they are embedded in thepiezoelectric/electrostrictive layer 26. In this structure, the firstelectrode 28 and the second electrode 30 are mutually opposed to oneanother in an alternate manner with a gap 29 having a constant widthinterposed therebetween.

The piezoelectric/electrostrictive elements 24 a, 24 b as shown in FIGS.10 and 11 can be preferably used for the piezoelectric/electrostrictivedevice 10A according to the first embodiment as well. When the pair ofcomb-shaped electrodes 28, 30 are used as in thepiezoelectric/electrostrictive elements 24 a, 24 b shown in FIGS. 10 and11, the displacement of the piezoelectric/electrostrictive element 24 a,24 b can be increased by decreasing the pitch D of the comb teeth of therespective electrodes 28, 30.

The operation of the piezoelectric/electrostrictive device 10A accordingto the first embodiment will now be explained. At first, for example,when the two piezoelectric/electrostrictive elements 24 a, 24 b are inthe natural state, namely when both of thepiezoelectric/electrostrictive elements 24 a, 24 b do not make thedisplacement action, then the major axis m of thepiezoelectric/electrostrictive device 10A (major axis of the fixationsection) is substantially coincident with the central axis n of themovable section 20 as shown in FIG. 12.

Starting from this state, for example, a sine wave Wa, which has apredetermined bias electric potential Vb, is applied to the pair ofelectrodes 28, 30 of the first piezoelectric/electrostrictive element 24a as shown in a waveform figure shown in FIG. 13A, while a sine wave Wb,which has a phase different from that of the sine wave Wa by about 180°,is applied to the pair of electrodes 28, 30 of the secondpiezoelectric/electrostrictive element 24 b as shown in FIG. 13B.

The piezoelectric/electrostrictive layer 26 of the firstpiezoelectric/electrostrictive element 24 a makes the contractiondisplacement in the direction of the first principal surface at a stageat which, for example, a voltage having a maximum value is applied tothe pair of electrodes 28, 30 of the firstpiezoelectric/electrostrictive element 24 a. Accordingly, as shown inFIG. 14, for example, the stress is generated for the first thin platesection 16 a to bend the thin plate section 16 a, for example, in therightward direction as shown by the arrow A. Therefore, the first thinplate section 16 a is bent in the rightward direction. At this time, astate is given, in which no voltage is applied to the pair of electrodes28, 30 of the second piezoelectric/electrostrictive element 24 b.Therefore, the second thin plate section 16 b follows the bending of thefirst thin plate section 16 a, and it is bent in the rightwarddirection. As a result, the movable section 20 is displaced, forexample, in the rightward direction with respect to the major axis m ofthe piezoelectric/electrostrictive device 10A. The displacement amountis changed depending on the maximum value of the voltage applied to eachof the piezoelectric/electrostrictive elements 24 a, 24 b. For example,the larger the maximum value is, the larger the displacement amount is.

Especially, when a material having high coercive electric field isapplied as the constitutive material for thepiezoelectric/electrostrictive layer 26, it is also preferable that thebias electric potential is adjusted so that the level of the minimumvalue is a slightly negative level as depicted by waveforms indicated bytwo-dot chain lines in FIGS. 13A and 13B. In this case, for example, thestress, which is in the same direction as the bending direction of thefirst thin plate section 16 a, is generated in the second thin platesection 16 b by driving the piezoelectric/electrostrictive element (forexample, the second piezoelectric/electrostrictive element 24 b) towhich the negative level is applied. Accordingly, it is possible tofurther increase the displacement amount of the movable section 20. Inother words, when the waveforms indicated by the dashed lines in FIGS.13A and 13B are used, the device is allowed to have such a function thatthe piezoelectric/electrostrictive element 24 b or 24 a, to which thenegative level is applied, supports the piezoelectric/electrostrictiveelement 24 a or 24 b which principally makes the displacement action.

In the case of the piezoelectric/electrostrictive device 10Af shown inFIG. 8, the voltage (see the sine waveform Wa) shown in FIG. 13A isapplied, for example, to the piezoelectric/electrostrictive element 24 a1 and the piezoelectric/electrostrictive element 24 b 2 which arearranged on the diagonal line, and the voltage (see the sine waveformWb) shown in FIG. 13B is applied to the otherpiezoelectric/electrostrictive element 24 a 2 and the otherpiezoelectric/electrostrictive element 24 b 1.

As described above, in the piezoelectric/electrostrictive device 10Aaccording to the first embodiment, the minute displacement of thepiezoelectric/electrostrictive element 24 a, 24 b is amplified into thelarge displacement action by utilizing the bending of the thin platesection 16 a, 16 b, and it is transmitted to the movable section 20.Accordingly, it is possible to greatly displace the movable section 20with respect to the major axis m of the piezoelectric/electrostrictivedevice 10A.

Especially, in the first embodiment, the movable section 20 is providedwith the mutually opposing end surfaces 36 a, 36 b. In this arrangement,the gap 38 is provided between the mutually opposing end surfaces 36 a,36 b, or the member 40, which is lighter than the constitutive member ofthe movable section 20, is allowed to intervene between the mutuallyopposing end surfaces 36 a, 36 b. Accordingly, it is possible toeffectively realize the light weight of the movable section 20. Thus, itis possible to increase the resonance frequency without decreasing thedisplacement amount of the movable section 20.

The frequency herein indicates the frequency of the voltage waveformobtained when the movable section 20 is displaced rightwardly andleftwardly by alternately switching the voltage applied to the pair ofelectrodes 28, 30. The resonance frequency indicates the frequency atwhich the displacement amplitude of the movable section 20 is maximumwhen the predetermined sine wave voltage is applied.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the hybrid structure is provided, in which the pair of thinplate sections 16 a, 16 b are made of metal, and the other components,i.e., the movable section 20 and the fixation section 22 are made ofceramics. It is unnecessary that all of the parts are formed with thepiezoelectric/electrostrictive material which is a fragile materialhaving a relatively heavy weight. Therefore, the device has thefollowing advantages. That is, the device has the high mechanicalstrength, and it is excellent in handling performance, shock resistance,and moisture resistance. Further, the operation of the device isscarcely affected by harmful vibration (for example, noise vibration andresidual vibration during high speed operation).

Further, in this embodiment, when the gap 38 is formed between themutually opposing end surfaces 36 a, 36 b, the part 20A of the movablesection 20 including the first end surface 36 a and the other part 20Bof the movable section 20 including the second end surface 36 b areeasily bent, resulting in strong resistance to the deformation.Accordingly, the piezoelectric/electrostrictive device 10A is excellentin handling performance.

The surface area of the movable section 20 or the fixation section 22 isincreased owing to the presence of the mutually opposing end surfaces 36a, 36 b. Therefore, as shown in FIG. 1, when the movable section 20 hasthe mutually opposing end surfaces 36 a, 36 b, the attachment area canbe increased when another part is attached to the movable section 20.Thus, it is possible to improve the attachment performance for the part.It is now assumed that the part is secured, for example, with anadhesive or the like. In this case, the adhesive is fully distributed tothe end surfaces 36 a, 36 b as well as to the first principal surface(attachment surface for the part) of the movable section 20. Therefore,it is possible to dissolve, for example, shortage of application of theadhesive. Thus, it is possible to reliably secure the part.

As an example of such an arrangement, FIG. 15 is illustrative of a casein which another piezoelectric/electrostrictive device according to theembodiment of the present invention (secondpiezoelectric/electrostrictive device 10A2) is secured to the movablesection 20 of the piezoelectric/electrostrictive device according to theembodiment of the present invention (firstpiezoelectric/electrostrictive device 10A1).

The first piezoelectric/electrostrictive device 10A1 has its fixationsection 22 which is secured to the surface of a base plate 122 by theaid of an adhesive 120. The fixation section 22 of the secondpiezoelectric/electrostrictive device 10A2 is secured to the movablesection 20 of the first piezoelectric/electrostrictive device 10A1 bythe aid of an adhesive 124. That is, in this arrangement, the twopiezoelectric/electrostrictive devices 10A1, 10A2 are arranged inseries. A member 126 having a light weight, which is different from themovable section 20, is allowed to intervene between the mutuallyopposing end surfaces 36 a, 36 b of the movable section 20 of the secondpiezoelectric/electrostrictive device 10A2.

In this case, the adhesive 124 for securing the secondpiezoelectric/electrostrictive device 10A2 is fully distributed up tothe space between the end surfaces 36 a, 36 b of the movable section 20of the first piezoelectric/electrostrictive device 10A1. Accordingly,the second piezoelectric/electrostrictive device 10A2 is tightly securedto the first piezoelectric/electrostrictive device 10A1. When thepiezoelectric/electrostrictive device 10A2 is bonded as described above,the light weight member (adhesive 124 in this case), which is differentfrom the movable section 20, is allowed to intervene between the endsurfaces 36 a, 36 b simultaneously with the adhesion. Therefore, thisarrangement is advantageous in that the production step can besimplified.

On the other hand, as shown in FIG. 3, when the fixation section 22 hasthe mutually opposing end surfaces 36 a, 36 b, it is possible to tightlyfix the piezoelectric/electrostrictive device 10Ab according to thesecond modified embodiment to a predetermined fixation portion, inaddition to the effect obtained when the movable section 20 has themutually opposing end surfaces 36 a, 36 b as described above. Thus, itis possible to improve the reliability.

In the first embodiment, the portion (substantial driving portion 18),at which the pair of electrodes 28, 30 are overlapped with each otherwith the piezoelectric/electrostrictive layer 26 interposedtherebetween, is continuously formed over the range from the part of thefixation section 22 to the part of the thin plate section 16 a, 16 b. Ifthe substantial driving portion 18 is formed to further extend over apart of the movable section 20, then it is feared that the displacementaction of the movable section 20 is restricted by the substantialdriving portion 18, and it is impossible to obtain the largedisplacement. However, in this embodiment, the substantial drivingportion 18 is formed such that it does not range over the movablesection 20. Therefore, it is possible to avoid the inconvenience of therestriction of the displacement action of the movable section 20, and itis possible to increase the displacement amount of the movable section20.

On the other hand, when the piezoelectric/electrostrictive element 24 a,24 b is formed on the part of the movable section 20, it is preferablethat the substantial driving portion 18 is located over the range fromthe part of the movable section 20 to the part of the thin plate section16 a, 16 b, because of the following reason. That is, if the substantialdriving portion 18 is formed to extend up to a part of the fixationsection 22, the displacement action of the movable section 20 isrestricted as described above.

Next, explanation will be made for preferred illustrative constructionsof the piezoelectric/electrostrictive device 10A according to the firstembodiment.

At first, in order to ensure the displacement action of the movablesection 20, it is preferable that the distance g, by which thesubstantial driving portion 18 of the piezoelectric/electrostrictiveelement 24 a, 24 b is overlapped with the fixation section 22 or themovable section 20, is not less than ½ of the thickness d of the thinplate section 16 a, 16 b.

The device is constructed such that the ratio a/b between the distance(distance in the X axis direction) a between the inner walls of the thinplate sections 16 a, 16 b and the width (distance in the Y axisdirection) b of the thin plate section 16 a, 16 b is 0.5 to 20. Theratio a/b is preferably 1 to 15 and more preferably 1 to 10. Theprescribed value of the ratio a/b is prescribed on the basis of thediscovery that the displacement amount of the movable section 20 isincreased to make it possible to dominantly obtain the displacement inthe X-Z plane.

On the other hand, it is desirable that the ratio e/a between the length(distance in the Z axis direction) e of the thin plate section 16 a, 16b and the distance a between the inner walls of the thin plate sections16 a, 16 b is preferably 0.5 to 10 and more preferably 0.5 to 5.

Further, it is preferable that the hole 12 is filled with a gelmaterial, for example, silicone gel. Usually, the displacement action ofthe movable section 20 is restricted by the presence of such a fillermaterial. However, in the first embodiment, it is intended to realizethe light weight brought about by the formation of the end surfaces 36a, 36 b on the movable section 20 and increase the displacement amountof the movable section 20. Therefore, the restriction of thedisplacement action of the movable section 20 due to the filler materialis counteracted. Accordingly, it is possible to realize the effect owingto the presence of the filler material, namely the realization of thehigh resonance frequency and the maintenance of the rigidity.

It is preferable that the length (distance in the Z axis direction) f ofthe movable section 20 is short, because of the following reason. Thatis, it is possible to realize the light weight and increase theresonance frequency by shortening the length. However, in order toensure the rigidity of the movable section 20 in the X axis directionand obtain its reliable displacement, it is desirable that the radio f/dwith respect to the thickness d of the thin plate section 16 a, 16 b isnot less than 2, and preferably not less than 5.

The actual size of each component is determined considering, forexample, the joining area for attaching the part to the movable section20, the joining area for attaching the fixation section 22 to anothermember, the joining area for attaching the electrode terminal or thelike, and the strength, the durability, the necessary displacementamount, the resonance frequency, and the driving voltage of the entirepiezoelectric/electrostrictive device 10A.

Specifically, for example, the distance a between the inner walls of thethin plate sections 16 a, 16 b is preferably 100 μm to 2000 μn and morepreferably 200 μm to 1600 μm. The width b of the thin plate section 16a, 16 b is preferably 50 μm to 2000 μm and more preferably 100 μm to 500μm. The thickness d of the thin plate section 16 a, 16 b is preferably 2μm to 100 μm and more preferably 10 μm to 80 μm, while it satisfies b>din relation to the width b of the thin plate section 16 a, 16 b, inorder to make it possible to effectively suppress the flappingdisplacement which is the displacement component in the Y axisdirection.

The length e of the thin plate section 16 a, 16 b is preferably 200 μmto 3000 μm and more preferably 300 μm to 2000 μm. The length f of themovable section 20 is preferably 50 μm to 2000 μm and more preferably100 μm to 1000 μm.

The arrangement as described above exhibits such an extremely excellenteffect that the displacement in the Y axis direction does not exceed 10%with respect to the displacement in the X axis direction, while thedevice can be driven at a low voltage by appropriately making adjustmentwithin the range of the size ratio and the actual size, and it ispossible to suppress the displacement component in the Y axis directionto be not more than 5%. In other words, the movable section 20 isdisplaced in one axis direction, i.e., substantially in the X axisdirection. Further, the high speed response is excellent, and it ispossible to obtain the large displacement at a relatively low voltage.

In the piezoelectric/electrostrictive device 10A, the shape of thedevice is unlike a conventional device, i.e., not the plate-shapedconfiguration where thickness is small in the direction perpendicular tothe displacement direction. Each of the movable section 20 and thefixation section 22 has the approximately rectangularparallelepiped-shaped configuration. The pair of thin plate sections 16a, 16 b are provided so that the side surface of the movable section 20is continuous to the side surface of the fixation section 22. Therefore,it is possible to selectively increase the rigidity ofpiezoelectric/electrostrictive device 10A in the Y axis direction.

That is, in the piezoelectric/electrostrictive device 10A, it ispossible to selectively generate only the operation of the movablesection 20 in the plane (XZ plane). It is possible to suppress theoperation of the movable section 20 in the YZ plane (operation in theso-called flapping direction).

Next, explanation will be made for the respective constitutivecomponents of the piezoelectric/electrostrictive device 10A according tothe first embodiment.

As described above, the movable section 20 is the portion which isoperated on the basis of the driving amount of the thin plate section 16a, 16 b, and a variety of members are attached thereto depending on thepurpose of use of the piezoelectric/electrostrictive device 10A. Forexample, when the piezoelectric/electrostrictive device 10A is used as adisplacement element, a shield plate for an optical shutter or the likeis attached thereto. Especially, when the piezoelectric/electrostrictivedevice 10A is used for the mechanism for positioning a magnetic head ofa hard disk drive or for suppressing the ringing, a member required tobe positioned is attached thereto, including, for example, the magnetichead, a slider provided with the magnetic head, and a suspensionprovided with the slider.

As described above, the fixation section 22 is the portion forsupporting the thin plate sections 16 a, 16 b and the movable section20. For example, in the case of the utilization to position the magnetichead of the hard disk drive, the entire piezoelectric/electrostrictivedevice 10A is fixed by supporting and fixing the fixation section 22,for example, to a carriage arm attached to VCM (voice coil motor) or afixation plate or a suspension attached to the carriage arm. As shown inFIG. 1, the terminals 32, 34 for driving thepiezoelectric/electrostrictive elements 24 a, 24 b and other members arearranged on the fixation section 22 in some cases.

The material for constructing the movable section 20 and the fixationsection 22 is not specifically limited provided that it has rigidity.However, it is possible to preferably use ceramics to which the ceramicgreen sheet-laminating method is applicable as described later on.Specifically, the material includes, for example, materials containing amajor component of zirconia represented by fully stabilized zirconia andpartially stabilized zirconia, alumina, magnesia, silicon nitride,aluminum nitride, and titanium oxide, as well as materials containing amajor component of a mixture of them. However, in view of the highmechanical strength and the high toughness, it is preferable to use amaterial containing a major component of zirconia, especially fullystabilized zirconia and a material containing a major component ofpartially stabilized zirconia. The metal material is not limitedprovided that it has rigidity. However, the metal material includes, forexample, stainless steel, nickel, brass, cupronickel, and bronze.

Those which are fully stabilized or partially stabilized as follows arepreferably used as fully stabilized zirconia or partially stabilizedzirconia as described above. That is, the compound to be used for fullystabilizing or partially stabilizing zirconia includes yttrium oxide,ytterbium oxide, cerium oxide, calcium oxide, and magnesium oxide. Whenat least one compound of them is added and contained, zirconia ispartially or fully stabilized. However, as for the stabilization, theobjective zirconia can be stabilized not only by adding one type of thecompound but also by adding a combination of the compounds.

The amount of addition of each of the compounds is desirably as follows.That is, yttrium oxide or ytterbium oxide is added by 1 to 30 mole %,preferably 1.5 to 10 mole %. Cerium oxide is added by 6 to 50 mole %,preferably 8 to 20 mole %. Calcium oxide or magnesium oxide is added by5 to 40 mole %, preferably 5 to 20 mole %. Especially, it is preferableto use yttrium oxide as a stabilizer. In this case, yttrium oxide isdesirably added by 1.5 to 10 mole %, more preferably 2 to 4 mole %. Forexample, alumina, silica, or transition metal oxide may be added as anadditive of sintering aid or the like in a range of 0.05 to 20% byweight. However, when the sintering integration based on the filmformation method is adopted as a technique for forming thepiezoelectric/electrostrictive element 24 a, 24 b, it is also preferableto add, for example, alumina, magnesia, and transition metal oxide as anadditive.

In order to obtain the mechanical strength and the stable crystal phase,it is desirable that the average crystal grain size of zirconia is 0.05to 3 μm, preferably 0.05 to 1 μm. As described above, ceramics can beused for the thin plate section 16 a, 16 b in the same manner as in themovable section 20 and the fixation section 22. Preferably, it isadvantageous to construct the thin plate sections 16 a, 16 b with asubstantially identical material in view of the reliability of thejoined portion and the strength of the piezoelectric/electrostrictivedevice 10A in order to reduce any complicated procedure of theproduction.

As described above, the thin plate section 16 a, 16 b is the portionwhich is driven in accordance with the displacement of thepiezoelectric/electrostrictive element 24 a, 24 b. The thin platesection 16 a, 16 b is the thin plate-shaped member having flexibility,and it functions to amplify the expansion and contracting displacementof the piezoelectric/electrostrictive element 24 a, 24 b arranged on thesurface as the bending displacement and transmit the displacement to themovable section 20. Therefore, it is enough that the shape or thematerial of the thin plate section 16 a, 16 b provides the flexibilitywith the mechanical strength of such a degree that it is not broken bythe bending displacement. It is possible to make appropriate selectionconsidering the response performance and the operability of the movablesection 20.

It is preferable that the thickness d of the thin plate section 16 a, 16b is preferably about 2 μm to 100 μm. It is preferable that the combinedthickness of the thin plate section 16 a, 16 b and thepiezoelectric/electrostrictive element 24 a, 24 b is 7 μm to 500 μm. Itis preferable that the thickness of the electrode 28, 30 is 0.1 to 50μm, and the thickness of the piezoelectric/electrostrictive layer 26 is3 to 300 μm. The width b of the thin plate section 16 a, 16 b ispreferably 50 μm to 2000 μm.

On the other hand, as for the shape and the material for the thin platesection 16 a, 16 b, it is enough to use those having the flexibility andhaving the mechanical strength of such a degree that no breakage occursdue to the bending displacement. Metal is preferably used. In this case,as described above, it is preferable to use a metal material which hasthe flexibility and which is capable of the bending displacement.Specifically, it is preferable to use a metal material which has aYoung's modulus of not less than 100 GPa.

Preferably, it is desirable that the thin plate section 16 a, 16 b ismade of an iron-based material such as various spring steel materials,marageing stainless steel materials, and stainless steel materialsincluding, for example, austenite-based stainless steel materials suchas SUS301, SUS304, AISI653, and SUH660, ferrite-based stainless steelmaterials such as SUS430 and SUS434, maltensite-based stainless steelmaterials such as SUS410 and SUS630, and semiaustenite-based stainlesssteel materials such as SUS631 and AISI632. Alternatively, it isdesirable that the thin plate section 16 a, 16 b is made of anon-ferrous material such as superelastic titanium alloy represented bytitanium-nickel alloy, brass, cupronickel, aluminum, tungsten,molybdenum, beryllium copper, phosphor bronze, nickel, nickel-ironalloy, and titanium.

When ceramics is used for the thin plate section 16 a, 16 b in the samemanner as the movable section 20 a, 20 b and the fixation section 22, itis preferable to use zirconia. Especially, a material containing a majorcomponent of fully stabilized zirconia and a material containing a majorcomponent of partially stabilized zirconia are used most preferably,because of the large mechanical strength even in the case of the thinwall thickness, the high toughness, and the small reactivity with thepiezoelectric/electrostrictive layer 26 and the electrode material.

The piezoelectric/electrostrictive element 24 a, 24 b has at least thepiezoelectric/electrostrictive layer 26 and the pair of electrodes 28,30 for applying the electric field to the piezoelectric/electrostrictivelayer 26. It is possible to use, for example,piezoelectric/electrostrictive elements of the unimorph type and thebimorph type. However, those of the unimorph type combined with the thinplate section 16 a, 16 b are suitable for thepiezoelectric/electrostrictive device 10A as described above, becausethey are excellent in stability of the generated displacement amount andthey are advantageous to realize the light weight.

For example, as shown in FIG. 1, it is possible to preferably use, forexample, the piezoelectric/electrostrictive element comprising the firstelectrode 28, the piezoelectric/electrostrictive layer 26, and thesecond electrode 30 which are stacked in the layered configuration.Additionally, it is also preferable to provide the multiple stagestructure as shown in FIGS. 5 to 9. In this arrangement, the positionaldiscrepancy of the film (electrode film) for constructing the electrode28, 30, i.e., for example, the positional discrepancy of the electrode28 in the in-plane direction on the perpendicular projection planedisposed as every other layer is not more than 50 μm. This facts alsoholds for the electrode 30.

As shown in FIG. 1, the piezoelectric/electrostrictive element 24 a, 24b is preferably formed on the outer surface side of thepiezoelectric/electrostrictive device 10A in view of the fact that thethin plate sections 16 a, 16 b can be driven to a greater extent.However, the piezoelectric/electrostrictive element 24 a, 24 b may beformed on the inner surface side of the piezoelectric/electrostrictivedevice 10A, i.e., on the inner wall surface of the hole 12 depending on,for example, the form of use. Alternatively, thepiezoelectric/electrostrictive elements 24 a, 24 b may be formed both onthe outer surface side and on the inner surface side of thepiezoelectric/electrostrictive device 10A.

Piezoelectric ceramics is preferably used for thepiezoelectric/electrostrictive layer 26. However, it is also possible touse electrostrictive ceramics, ferroelectric ceramics, oranti-ferroelectric ceramics. However, when thepiezoelectric/electrostrictive device 10A is used, for example, toposition the magnetic head of the hard disk drive, it is important toprovide the linearity concerning the displacement amount of the movablesection 20 and the driving voltage or the output voltage. Therefore, itis preferable to use a material having small strain hysteresis. It ispreferable to use a material having a coercive electric field of notmore than 10 kV/mm.

Specified materials include ceramics containing, for example, leadzirconate, lead titanate, lead magnesium niobate, lead nickel niobate,lead zinc niobate, lead manganese niobate, lead antimony stannate, leadmanganese tungstate, lead cobalt niobate, barium titanate, sodiumbismuth titanate, potassium sodium niobate, and strontium bismuthtantalate singly or in mixture.

Especially, a material containing a major component of lead zirconate,lead titanate, and lead magnesium niobate, or a material containing amajor component of sodium bismuth titanate is preferably used, in orderto obtain the product having a stable composition with a highelectromechanical coupling factor and a piezoelectric constant and withsmall reactivity with the thin plate sections 16 a, 16 b (ceramics) whenthe thin plate section 16 a, 16 b is made of ceramics, and thepiezoelectric/electrostrictive layer 26 is sintered in an integratedmanner.

It is also preferable to use ceramics obtained by adding, to thematerial described above, for example, oxides of lanthanum, calcium,strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,manganese, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium,tantalum, lithium, bismuth, and stannum, or compounds each containing atleast one component to be finally formed into oxide, singly or inmixture.

For example, when lanthanum and/or strontium is contained in the majorcomponents of lead zirconate, lead titanate, and lead magnesium niobate,an advantage is obtained in some cases, for example, in such a way thatthe coercive electric field and the piezoelectric characteristic can beadjusted.

It is desirable to avoid the addition of a material such as silica whichtends to form glass, because of the following reason. That is, thematerial such as silica tends to react with thepiezoelectric/electrostrictive material during the heat treatment forthe piezoelectric/electrostrictive layer. As a result, the compositionis varied, and the piezoelectric characteristic is deteriorated.

On the other hand, it is preferable that the pair of electrodes 28, 30of the piezoelectric/electrostrictive element 24 a, 24 b are made ofmetal which is solid at room temperature and which is excellent inconductivity. For example, it is possible to use metal simple substanceor alloy of, for example, aluminum, titanium, chromium, iron, cobalt,nickel, copper, zinc, niobium, molybdenum, ruthenium, palladium,rhodium, silver, stannum, tantalum, tungsten, iridium, platinum, gold,and lead. It is also preferable to use a cermet material obtained bydispersing, in the metal described above, ceramics of the same materialas that of the piezoelectric/electrostrictive layer 26 or the materialdifferent from that of the piezoelectric/electrostrictive layer 26.

The material for the electrodes 28, 30 of thepiezoelectric/electrostrictive element 24 a, 24 b is selected anddetermined depending on the method for forming thepiezoelectric/electrostrictive layer 26. For example, when thepiezoelectric/electrostrictive layer 26 is formed by sintering on thefirst electrode 28 after the first electrode 28 is formed on the thinplate section 16 a, 16 b, it is necessary for the first electrode 28 touse high melting point metal such as platinum, palladium,platinum-palladium alloy, and silver-palladium alloy which does notchange at the sintering temperature for thepiezoelectric/electrostrictive layer 26. However, the electrodeformation can be performed at a low temperature for the second electrode30 which is formed on the piezoelectric/electrostrictive layer 26 whenit is located at the outermost layer after forming thepiezoelectric/electrostrictive layer 26. Therefore, it is possible forthe second electrode 30 to use low melting point metal such as aluminum,gold, and silver.

When the stacked type piezoelectric/electrostrictive element 24 is stuckto the thin plate section 16 a, 16 b by the aid of the adhesive 202, itis preferable that the piezoelectric/electrostrictive layer 26 and theelectrodes 28, 30 (electrode films) are stacked and integrated into oneunit in a multilayered configuration, and then they are collectivelysintered. In this case, high melting point metal such as platinum,palladium, and alloy thereof is used for the electrodes 28, 30. It ispreferable that the electrode 28, 30 is made of cermet as a mixture ofthe high melting point metal and the piezoelectric/electrostrictivematerial or another ceramic.

The thickness of the electrode 28, 30 also serves as a factor toconsiderably decrease the displacement of thepiezoelectric/electrostrictive element 24 a, 24 b. Therefore, it ispreferable, especially for the electrode formed after the sintering ofthe piezoelectric/electrostrictive layer 26, to use organic metal pastecapable of obtaining a dense and thinner film after sintering, forexample, a material such as gold resinate paste, platinum resinatepaste, and silver resinate paste.

Next, explanation will be made with reference to FIGS. 16A to 23 forseveral methods for producing the piezoelectric/electrostrictive device10A according to the first embodiment.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the thin plate section 16 a, 16 b is made of metal, and theconstitutive material for each of the movable section 20 and thefixation section 22 is ceramics. Therefore, it is preferable that theconstitutive elements of the piezoelectric/electrostrictive device 10Aconcerning the fixation section 22 and the movable section 20, exceptfor the thin plate sections 16 a, 16 b and thepiezoelectric/electrostrictive elements 24 a, 24 b, are produced byusing the ceramic green sheet-laminating method. On the other hand, itis preferable that the piezoelectric/electrostrictive elements 24 a, 24b as well as the respective terminals 32, 34 are produced by using thefilm formation method, for example, for the thin film and the thickfilm.

The thin plate sections 16 a, 16 b are preferably secured to the sidesurfaces of the movable section 20 and the fixation section 22 by theaid of the adhesive 200. The piezoelectric/electrostrictive element 24a, 24 b is preferably secured onto the thin plate section 16 a, 16 b bythe aid of the adhesive 202.

According to the ceramic green sheet-laminating method in which themovable section 20 and the fixation section 22 of thepiezoelectric/electrostrictive device 10A can be formed in an integratedmanner, the time-dependent change of state scarcely occurs at the joinedportions of the respective members. Therefore, this method provides thehigh reliability of the joined portion, and it is advantageous to ensurethe rigidity.

In the piezoelectric/electrostrictive device 10A according to the firstembodiment, the boundary portion between the thin plate section 16 a, 16b and the fixation section 22 and the boundary portion between the thinplate section 16 a, 16 b and the movable section 20 function assupporting points for expressing the displacement. Therefore, thereliability of each of the boundary portions is an important point whichdominates the characteristic of the piezoelectric/electrostrictivedevice 10A.

The production methods described below are excellent in productivity andformability. Therefore, it is possible to obtain thepiezoelectric/electrostrictive device having a predetermined shapewithin a short period of time with good reproducibility.

A first production method for the piezoelectric/electrostrictive device10A according to the first embodiment will be specifically explainedbelow. The following definitions are now made. The laminate, which isobtained by laminating the ceramic green sheets, is defined to be theceramic green laminate 158 (see, for example, FIG. 16B). The integratedmatter, which is obtained by sintering the ceramic green laminate 158into one unit, is defined to be the ceramic laminate 160 (see, forexample, FIG. 17A). The stuck or glued matter comprising the ceramiclaminate 160 and the metal plate is defined to be the hybrid laminate162 (see FIG. 18). The integrated matter comprising the movable section20, the thin plate sections 16 a, 16 b, and the fixation section 22,which is obtained by cutting off unnecessary portions from the hybridlaminate 162, is defined to be the substrate 14D (see FIG. 19).

In the first production method, the hybrid laminate 162 is finally cutinto chip units to produce a large number ofpiezoelectric/electrostrictive devices 10A. However, in order tosimplify the explanation, description will be made principally for thecase in which one individual of piezoelectric/electrostrictive device10A is produced.

At first, for example, a binder, a solvent, a dispersing agent, and aplasticizer are added and mixed with a ceramic powder such as zirconiato prepare a slurry. The slurry is subjected to a degassing treatment,and then a ceramic green sheet having a predetermined thickness isprepared in accordance with, for example, the reverse roll coater methodor the doctor blade method.

Subsequently, the ceramic green sheet is processed into those havingvarious shapes as shown in FIG. 16A in accordance with, for example, thepunching out based on the use of the mold or the laser machining toprepare a plurality of ceramic green sheets for forming the substrate.Specifically, a plurality (for example, four) of ceramic green sheets50A to 50D each of which is formed with a window 54 for forming at leastthe hole 12 thereafter, and a ceramic green sheet 102 which iscontinuously formed with a window 54 for forming the hole 12 thereafterand a window 100 for forming the movable section 20 having the mutuallyopposing end surfaces 36 a, 36 b are prepared.

After that, as shown in FIG. 16B, the ceramic green sheets 50A to 50D,102 are laminated and secured under pressure to form a ceramic greenlaminate 158. The lamination is performed while the ceramic green sheet102 is positioned at the center. After that, the ceramic green laminate158 is sintered to obtain a ceramic laminate 160 as shown in FIG. 17A.At this stage, the ceramic laminate 160 is formed such that the hole 130is formed by the windows 54, 100.

Subsequently, as shown in FIG. 17B, the piezoelectric/electrostrictiveelements 24 a, 24 b, which are constructed as separate members, arerespectively bonded with an epoxy adhesive 202 to the surfaces of metalplates 152A, 152B to serve as the thin plate sections.

Subsequently, the metal plates 152A, 152B are bonded to the ceramiclaminate 160 with an epoxy adhesive 200 so that the ceramic laminate 160is interposed between the metal plates 152A, 152B and the hole 130 isclosed thereby to provide a hybrid laminate 162 (see FIG. 18).

Subsequently, as shown in FIG. 18, the hybrid laminate 162, which isformed with the piezoelectric/electrostrictive elements 24 a, 24 b, iscut along cutting lines C1, C2, C5 to thereby cut off side portions andforward end portions of the hybrid laminate 162. As a result of thecutoff, as shown in FIG. 19, the piezoelectric/electrostrictive device10A according to the first embodiment is obtained, in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on thethin plate sections constituted by the metal plates, of the substrate14D, and the movable section 20 having the mutually opposing endsurfaces 36 a, 36 b is formed.

On the other hand, in the second production method, at first, as shownin FIG. 20A, a plurality (for example, four) of ceramic green sheets 50Ato 50D each of which is formed with a window 54 for forming at least thehole 12 thereafter, and a ceramic green sheet 102 which is continuouslyformed with a window 54 for forming the hole 12 thereafter and a window100 for forming the movable section 20 having the mutually opposing endsurfaces 36 a, 36 b are prepared.

After that, as shown in FIG. 20B, the ceramic green sheets 50A to 50D,102 are laminated and secured under pressure to form a ceramic greenlaminate 158. After that, the ceramic green laminate 158 is sintered toobtain a ceramic laminate 160 as shown in FIG. 21A. At this stage, theceramic laminate 160 is formed such that the hole 130 is formed by thewindows 54, 100.

Subsequently, as shown in FIG. 21B, the metal plates 152A, 152B arebonded to the ceramic laminate 160 with the epoxy adhesive 200 so thatthe ceramic laminate 160 is interposed between the metal plates 152A,152B and the hole 130 is closed thereby to provide a hybrid laminate162. In this procedure, when the piezoelectric/electrostrictive elements24 a, 24 b are affixed to the surfaces of the bonded metal plates 152A,152B, the hole 130 is optionally filled with a filler material 164 asshown in FIG. 21A so that a sufficient bonding pressure may be applied.

It is necessary to finally remove the filler material 164. Therefore, itis preferable to use a hard material which is easily dissolved in asolvent or the like. The material includes, for example, organic resinand wax. It is also possible to adopt a material obtained by mixingceramic powder as a filler with organic resin such as acrylic.

Subsequently, as shown in FIG. 21B, the piezoelectric/electrostrictiveelements 24 a, 24 b, which are constructed as separate members, arebonded with the epoxy adhesive 202 to the surfaces of the metal plates152A, 152B of the hybrid laminate 162. The separate members of thepiezoelectric/electrostrictive elements 24 a, 24 b can be formed, forexample, in accordance with the ceramic green sheet-laminating method orthe multilayer printing method.

Subsequently, as shown in FIG. 22, the hybrid laminate 162, which isformed with the piezoelectric/electrostrictive elements 24 a, 24 b, iscut along cutting lines C1, C2, C5 to thereby cut off side portions andforward end portions of the hybrid laminate 162. As a result of thecutoff, as shown in FIG. 23, the piezoelectric/electrostrictive device10A according to the first embodiment is obtained, in which thepiezoelectric/electrostrictive elements 24 a, 24 b are formed on thethin plate sections constituted by the metal plates, of the substrate14D, and the movable section 20 having the mutually opposing endsurfaces 36 a, 36 b is formed.

When all of the substrate section is made of metal, for example, theportions corresponding to the ceramic laminate 160 shown in FIG. 17A areformed by means of molding. Further, bulk-shaped members may be formedin accordance with the method of grinding machining, wire electricdischarge machining, mold stamping or punching out, or chemical etching,or metal materials having thin plate-shaped configurations may belaminated to form the substrate section in accordance with the claddingmethod.

Next, a piezoelectric/electrostrictive device 10B according to thesecond embodiment will be explained with reference to FIGS. 24 to 52.

As shown in FIG. 24, the piezoelectric/electrostrictive device 10Baccording to the second embodiment comprises a pair of mutually opposingthin plate sections 16 a, 16 b, and a fixation section 22 for supportingthe thin plate sections 16 a, 16 b. A stacked typepiezoelectric/electrostrictive element 24 is arranged on one thin platesection 16 a of the pair of thin plate sections 16 a, 16 b. In FIGS. 24and 25, the stacked type piezoelectric/electrostrictive element 24 isillustrated in a simplified manner, because its structure iscomplicated. Details are shown in magnified views of FIGS. 26 to 29.

The fixation section 22 is secured, for example, by the aid of anadhesive 200 between the respective rearward ends of the pair of thinplate sections 16 a, 16 b. The respective forward ends of the pair ofthin plate sections 16 a, 16 b are open ends.

As shown in FIG. 25, for example, the movable section 20 or variousparts and members are secured, for example, by the aid of the adhesive200 between the respective forward ends of the pair of thin platesections 16 a, 16 b. The example shown in FIG. 25 is illustrative of thecase in which the movable section 20, which is constructed by the samemember as that of the fixation section 22, is secured by the aid of theadhesive 200 between the respective forward ends of the pair of thinplate sections 16 a, 16 b.

Each of the pair of thin plate sections 16 a, 16 b is made of metal. Thefixation section 22 and the movable section 20 are made of ceramics ormetal. Especially, in the examples shown in FIGS. 24 and 25, thethickness of the first thin plate section 16 a on which the stacked typepiezoelectric/electrostrictive element 24 is formed, of the pair of thinplate sections 16 a, 16 b is larger than the thickness of the secondthin plate section 16 b.

The stacked type piezoelectric/electrostrictive element 24 is affixed tothe thin plate section 16 a by the aid of an adhesive 202 such asorganic resin, glass, brazing, soldering, and eutectic bonding. That is,the stacked type piezoelectric/electrostrictive element 24 is secured bythe adhesive 202 to the thin plate section 16 a made of metal to therebyconstruct an actuator section 204 which is the driving source of thepiezoelectric/electrostrictive device 10B.

In the piezoelectric/electrostrictive device 10B, the forward end(portion to which the movable section 20 is attached) of the thin platesection 16 a (16 a and 16 b in the example shown in FIG. 25) isdisplaced in accordance with the driving of the actuator section 204.Alternatively, the displacement of the forward end of the thin platesection 16 a is electrically detected by the aid of the actuator section204 (transducer section in the case of the use as a sensor). In thiscase, the device is utilized as a sensor.

As shown in FIG. 26, for example, the stacked typepiezoelectric/electrostrictive element 24 is constructed as follows.That is, each of the piezoelectric/electrostrictive layer 26 and thepair of electrodes 28, 30 has the multilayered structure, and the firstelectrodes 28 and the second electrodes 30 are alternately stackedrespectively to give the multiple stage structure at the portion atwhich the first electrodes 28 and the second electrodes 30 areoverlapped with each other with the piezoelectric/electrostrictive layer26 intervening therebetween.

In FIG. 26, each of the piezoelectric/electrostrictive layer 26 and thepair of electrodes 28, 30 has the multilayered structure. The firstelectrode 28 and the second electrode 30 are alternately stacked witheach other to give the substantially comb-shaped configuration. Themultiple stage structure is formed at the portion at which the firstelectrode 28 and the second electrode 30 are overlapped with each otherwith the piezoelectric/electrostrictive layer 26 interposedtherebetween.

Specifically, the stacked type piezoelectric/electrostrictive element 24has the approximately rectangular parallelepiped-shaped configuration,comprising a plurality of piezoelectric/electrostrictive layers 26 and aplurality of electrode films 28, 30. The electrode films 28, 30, whichcontact with the upper and lower surfaces of each of thepiezoelectric/electrostrictive layers 26, are alternately led toopposite end surfaces 208, 209 respectively. End surface electrodes 28c, 30 c, which electrically connect the respective electrode films 28,30 alternately led to the opposite end surfaces 208, 209, areelectrically connected to terminals 28 b, 30 b which are formed on thesurface of the outermost layer of the piezoelectric/electrostrictivelayer 26 and which are arranged while being separated from each other bya predetermined distance Dk.

It is preferable that the predetermined distance Dk between theterminals 28 b, 30 b is not less than 20 μm. Further, the material ofthe electrode films 28, 30 to make contact with the upper and lowersurfaces of the piezoelectric/electrostrictive layer may be differentfrom the material of the end surface electrodes 28 c, 30 c. Further, atleast one of the terminals (terminal 28 b in the example shown in FIG.26) and the end surface electrode 28 c corresponding to the terminal 28b may be electrically connected with a thin film electrode film (outersurface electrode) 28 d which is thinner than the terminal 28 b and theend surface electrode 28 c.

The surface electrode film 28 d, the end surface electrodes 28 c, 30 c,and the terminals 28 b, 30 b, which are formed after sintering thepiezoelectric/electrostrictive layer 26, may be thin, and they may havelow heat resistance, as compared with the electrode layers 28, 30 whichare formed before sintering the piezoelectric/electrostrictive layer 26or which are sintered simultaneously.

FIG. 26 is illustrative of the following case. That is, thepiezoelectric/electrostrictive layer 26 has the five-layered structure.The first electrodes 28 are formed in the comb-shaped configuration sothat they are disposed on the upper surface of the first layer, theupper surface of the third layer, and the upper surface of the fifthlayer. The second electrodes 30 are formed in the comb-shapedconfiguration so that they are disposed on the upper surface of thesecond layer and the upper surface of the fourth layer.

FIG. 28 is illustrative of the following case. That is, thepiezoelectric/electrostrictive layer 26 has the five-layered structureas well. The first electrodes 28 are formed in the comb-shapedconfiguration so that they are disposed on the upper surface of thefirst layer, the upper surface of the third layer, and the upper surfaceof the fifth layer. The second electrodes 30 are formed in thecomb-shaped configuration so that they are disposed on the lower surfaceof the first layer, the upper surface of the second layer, and the uppersurface of the fourth layer.

In the case of the structures described above, it is possible tosuppress the increase in number of terminals by connecting the mutualfirst electrodes 28 and the mutual second electrodes 30 with each otherto be common. Therefore, it is possible to suppress the increase insize, which would be otherwise caused when the stacked typepiezoelectric/electrostrictive element 24 is used.

As described above, the driving force of the actuator section 204 isincreased by using the stacked type piezoelectric/electrostrictiveelement 24, and thus it is possible to obtain the large displacement.Further, it is possible to realize the high resonance frequency byincreasing the rigidity of the piezoelectric/electrostrictive device 10Bitself. Thus, it is easy to achieve the high speed of the displacementaction.

When the number of stages is increased, it is possible to increase thedriving force of the actuator section 204. However, the electric powerconsumption is also increased in accordance therewith. Therefore, whenthe present invention is carried out, for example, the number of stagesmay be appropriately determined depending on the way of use and thestate of use. In the case of the piezoelectric/electrostrictive device10B according to the second embodiment, the width of the thin platesection 16 a, 16 b (distance in the Y axis direction) is basicallyunchanged, even when the driving force of the actuator section 204 isincreased, owing to the use of the stacked typepiezoelectric/electrostrictive element 24. Therefore, the device isextremely preferred to make application, for example, to the actuatorfor the purpose of the ringing control and the positioning of themagnetic head for the hard disk to be used in an extremely narrow gap.

The stacked type piezoelectric/electrostrictive element 24 is preferablyformed at the following position with respect to the thin plate section16 a. That is, the forward end 208 of the multilayered member forconstructing the stacked type piezoelectric/electrostrictive element 24is disposed at the position not including at least the fixation section22 as viewed in plan view (position included in the hole formed betweenthe movable section 20 and the fixation section 22 in the example shownin FIG. 25). The rearward end 209 of the multilayered member forconstructing the stacked type piezoelectric/electrostrictive element 24is disposed at the position including at least the fixation section 22as viewed in plan view. The end 28 b of the electrode 28 is formed atthe position including at least the fixation section 22 as viewed inplan view, and the end 30 a of the electrode 30 is formed at theposition not including the fixation section 22 as viewed in plan view(position included in the hole formed between the movable section 20 andthe fixation section 22 as well in the example shown in FIG. 25).

The voltage is applied to the pair of electrodes 28, 30 via ends(hereinafter referred to as “terminals 28 b, 30 b”) of the respectiveelectrodes 28, 30 formed on the fifth layer of thepiezoelectric/electrostrictive layer 30. The respective terminals 28 b,30 b are formed to be separated from each other in such a degree thatthey can be electrically insulated from each other.

The spacing distance Dk between the terminals 28 a, 30 b is preferablynot less than 20 μm, and it is preferably not less than 50 μm when thethickness of the terminal 28 b, 30 b is 1 μm to 30 μm. The terminals 28b, 30 b may be made of the same material as that of the internalelectrodes 28, 30, or they may be made of a material differenttherefrom. For example, the same material may be used when the terminals28 b, 30 b are co-fired with the piezoelectric/electrostrictive layer26. The different materials may be used when the sintering is performedseparately.

It is preferable for the end surface electrodes 28 c, 30 c that theinternal electrodes 28, 30 and the piezoelectric/electrostrictive layer26 are sintered, and then their end surfaces are subjected to, forexample, grinding and polishing to effect the electric connectionbetween the internal electrodes and the end surface electrodes. Thematerial of the end surface electrodes 28 c, 30 c may be the same as, ordifferent from that of the internal electrodes 28, 30. For example, itis preferable that platinum paste is utilized for the internalelectrodes 28, 30, gold resinate is utilized for the outer surfaceelectrode 28 d, and gold paste is utilized for the end surfaceelectrodes 28 c, 30 c and the terminals 28 b, 30 b. However, it is alsopossible to adopt approximately the same construction as that of thepiezoelectric/electrostrictive device according to the first embodimentdescribed above.

In this arrangement, the piezoelectric/electrostrictive device 10B canbe independently fixed by utilizing the surface other than the surfaceon which the terminals 28 b, 30 b are arranged. As a result, it ispossible to obtain high reliability for both of the fixation of thepiezoelectric/electrostrictive device 10B and the electric connectionbetween the circuit and the terminals 28 b, 30 b. In this arrangement,the electric connection between the terminals 28 b, 30 b and the circuitis made, for example, by means of the flexible printed circuit, theflexible flat cable, and the wire bonding.

As described above, in the piezoelectric/electrostrictive device 10Baccording to the second embodiment, the actuator section 204 isconstructed by securing the stacked type piezoelectric/electrostrictiveelement 24 onto the thin plate section 16 a made of metal by the aid ofthe adhesive 202. Therefore, it is possible to greatly displace the thinplate section 16 a (and 16 b) even when the a real size of the stackedtype piezoelectric/electrostrictive element 24 is not widened as viewedin plan view. Further, the thin plate section 16 a (and 16 b) is made ofmetal. Therefore, the device is excellent in strength and toughness, andit is possible to respond to the quick displacement action as well.

In other words, in the second embodiment, it is possible to sufficientlyrespond to the variation of environment of use and the severe state ofuse. The device is excellent in shock resistance. It is possible torealize the long service life of the piezoelectric/electrostrictivedevice 10B, and it is possible to improve the handling performance ofthe piezoelectric/electrostrictive device 10B. Further, the thin platesection can be greatly displaced at a relatively low voltage. Therigidity of the thin plate section 16 a (and 16 b) is high, the filmthickness of the actuator section 204 is thick, and the rigidity of theactuator section 204 is high. Accordingly, it is possible to achieve therealization of the high speed (realization of the high resonancefrequency) of the displacement action of the thin plate section 16 a(and 16 b).

Usually, in order to drive, at a high speed, the actuator section 204constructed by combining the thin plate section 16 a and thepiezoelectric/electrostrictive element 24 which makes straindeformation, it is necessary to increase the rigidity of the actuatorsection 204. In order to obtain large displacement, it is necessary todecrease the rigidity of the actuator section 204.

However, in the piezoelectric/electrostrictive device 10B according tothe second embodiment, the thin plate sections 16 a, 16 b, whichconstitute the actuator section 204, are opposed to one another toprovide the pair of thin plate sections 16 a, 16 b. The fixation section22 is secured by the adhesive 200 between the respective rearward endsof the pair of thin plate sections 16 a, 16 b to construct the multiplestage structure of the piezoelectric/electrostrictive element 24. Theposition of the piezoelectric/electrostrictive element 24, the materialand the size of the constitutive members are appropriately selected toconstruct the piezoelectric/electrostrictive device 10B. Therefore, itis possible to effect the both of the contradicting characteristics asdescribed above. When the object, which has substantially the samedegree of size as that of the fixation section 22, intervenes betweenthe open ends of the pair of thin plate sections 16 a, 16 b, the minimumresonance frequency of the structure is not less than 20 kHz. Further,the relative displacement amount concerning the object and the fixationsection 22 can be not less than 0.5 μm at a substantial applied voltageof 30 V at a frequency which is not more than ¼ of the resonancefrequency.

As a result, it is possible to greatly displace the pair of thin platesections 16 a, 16 b. Further, it is possible to achieve the realizationof the high speed (realization of the high resonance frequency) of thedisplacement action of the piezoelectric/electrostrictive device 10B,especially of the pair of thin plate sections 16 a, 16 b.

In the piezoelectric/electrostrictive device 10B according to the secondembodiment, the minute displacement of thepiezoelectric/electrostrictive element 24 is amplified into the largedisplacement action by utilizing the bending of the thin plate sections16 a, 16 b, and it is transmitted to the movable section 20. Therefore,the movable section 20 can be greatly displaced with respect to themajor axis m (see FIG. 14) of the piezoelectric/electrostrictive device10B.

In the piezoelectric/electrostrictive device 10B according to the secondembodiment, it is unnecessary that all of the parts are formed with thepiezoelectric/electrostrictive material which is a fragile materialhaving a relatively heavy weight. Therefore, the device has thefollowing advantages. That is, the device has the high mechanicalstrength, and it is excellent in handling performance, shock resistance,and moisture resistance. Further, the operation of the device isscarcely affected by harmful vibration (for example, noise vibration andresidual vibration during high speed operation).

Further, as shown in FIG. 24, the forward ends of the pair of thin platesections 16 a, 16 b are the open ends. Accordingly, when various membersor parts are attached to the piezoelectric/electrostrictive device 10B,it is possible to utilize the forward ends of the pair of thin platesections 16 a, 16 b. The member or the part can be attached in such away that the member or the part is interposed by the forward ends. Inthis case, it is possible to provide a large attachment area for themember or the part, and it is possible to improve the attachmentperformance for the part. Further, the member or the part to be attachedis consequently included in the pair of thin plate sections 16 a, 16 b.Therefore, it is possible to decrease the size of thepiezoelectric/electrostrictive device in the Y direction after attachingthe member or the part. Thus, the device is advantageous to realize thecompact size.

Of course, as shown in FIG. 25, when the movable section 20 is securedbetween the respective forward ends of the pair of thin plate sections16 a, 16 b, then various members or parts are secured, for example, bythe aid of an adhesive to the first principal surface of the movablesection 20.

In the second embodiment, the forward end 208 of the multilayered memberfor constructing the stacked type piezoelectric/electrostrictive element24 is disposed at the position not including at least the fixationsection 22 as viewed in plan view. The rearward end of the multilayeredmember is disposed at the position including at least the fixationsection 22 as viewed in plan view. The end 28 a of the electrode 28 isdisposed at the position including at least the fixation section 22 asviewed in plan view. The end 30 a of the electrode 30 is disposed at theposition not including the fixation section 22 as viewed in plan view.

For example, if the respective ends of the pair of electrodes 28, 30 areformed at the position included in the movable section 20, then it isfeared that the displacement action of the pair of thin plate sections16 a, 16 b is restricted by the stacked typepiezoelectric/electrostrictive element 24, and it is impossible toobtain the large displacement. However, in the second embodiment, theforegoing positional relationship is adopted. Therefore, it is possibleto avoid the inconvenience of the restriction of the displacement actionof the movable section 20, and it is possible to increase thedisplacement amount of the pair of thin plate sections 16 a, 16 b.

Next, explanation will be made for preferred illustrative constructionsof the piezoelectric/electrostrictive device 10B according to the secondembodiment. The preferred illustrative constructions are approximatelythe same as those of the piezoelectric/electrostrictive device accordingto the first embodiment described above. Therefore, explanation will bemade for only the preferred illustrative constructions inherent in thepiezoelectric/electrostrictive device 10B according to the secondembodiment.

At first, in the piezoelectric/electrostrictive device 10B according tothe second embodiment, the shape of the device 10B is not theplate-shaped configuration unlike the conventional one. When the movablesection 20 is provided, the movable section 20 and the fixation section22 form the rectangular parallelepiped-shaped configuration. The pair ofthin plate sections 16 a, 16 b are provided so that the side surfaces ofthe movable section 20 and the fixation section 22 are continuous togive the rectangular annular configuration. Therefore, it is possible toselectively enhance the rigidity of the piezoelectric/electrostrictivedevice 10B in the Y axis direction.

That is, in the piezoelectric/electrostrictive device 10B, it ispossible to selectively generate only the action of the movable section20 in the plane (in the XZ plane). It is possible to suppress the actionof the pair of thin plate sections in the YZ plane (action in theso-called flapping direction).

It is desirable that the thin plate sections 16 a, 16 b are made ofmetal. The fixation section 22 and the movable section 20 may be made ofmaterials of different types, but they are more preferably made ofmetal. For example, organic resin, brazing material, or solder may beused to bond the thin plate sections 16 a, 16 b to the fixation section22 and bond the thin plate sections 16 a, 16 b to the movable section20. However, it is more preferable to form an integrated structureformed by diffusion joining or welding between metal materials. It ismore desirable to use metal subjected to the cold rolling process,because of the high strength owing to the presence of a great degree ofdislocation.

In the second embodiment, the stacked typepiezoelectric/electrostrictive element 24 is formed on only one thinplate section 16 a. Therefore, the device can be produced inexpensivelyas compared with a device (modified embodiment) in which the stackedtype piezoelectric/electrostrictive elements 24 a, 24 b are formed onthe pair of thin plate sections 16 a, 16 b respectively as shown in FIG.30. Further, in the second embodiment, when the observation is made in astate in which the movable section 20 is secured, then the thin platesection 16 a having the large thickness, on which the stacked typepiezoelectric/electrostrictive element 24 is formed, is directlydisplaced, and the thin plate section 16 b having the thin thickness, onwhich the stacked type piezoelectric/electrostrictive element 24 is notformed, is displaced in cooperation therewith. Accordingly, it ispossible to cause the displacement to a greater extent.

The formation of the stacked type piezoelectric/electrostrictive element24 on the thin plate section 16 a can be realized by bonding the stackedtype piezoelectric/electrostrictive element 24 to the thin plate section16 a, for example, with organic resin, brazing material, or solder. Whenthe element is bonded at a low temperature, it is desirable to useorganic resin. When the element is allowed to be bonded at a hightemperature, it is preferable to use, for example, brazing material,solder, and glass. However, the coefficient of thermal expansiongenerally differs among the thin plate section 16 a, the stacked typepiezoelectric/electrostrictive element 24, and the adhesive 202.Therefore, it is desirable that the bonding temperature is low in ordernot to generate any stress in the stacked typepiezoelectric/electrostrictive element 24 due to the difference incoefficient of thermal expansion. In the case of organic resin, thebonding can be generally effected at a temperature of not more than 180°C. Therefore, organic resin is preferably adopted. More preferably, itis desirable to use a room temperature setting adhesive. When thefixation of the thin plate section 16 a, 16 b and thepiezoelectric/electrostrictive element 24 is performed simultaneouslywith, or after the fixation of the fixation section 22, the movablesection 20, and the thin plate section 16 a, 16 b, if the fixationsection 22 or the movable section 20 has the open type structure, thenit is possible to effectively reduce the strain which would be otherwisecaused between the different types of materials.

In order not to exert any thermal stress on the stacked typepiezoelectric/electrostrictive element 24, it is preferable that thestacked type piezoelectric/electrostrictive element 24 is bonded to thethin plate section 16 a with organic resin, and the fixation isperformed in separate steps for the thin plate sections 16 a, 16 b, thefixation section 22, and the movable section 20.

As shown in FIG. 31, when the part of the piezoelectric/electrostrictiveelement 24 is located at the fixation section 22, it is preferable that(1−Lb/La) is not less than 0.4, and more preferably 0.5 to 0.8 providedthat La represents a shortest distance concerning the pair of thin platesections 16 a, 16 b between a boundary portion with respect to themovable section 20 and a boundary portion with respect to the fixationsection 22, and Lb represents a shortest distance of distances from theboundary portion between the thin plate section 16 a and the movablesection 20 to any one of the ends 28 a, 30 a of the pair of electrodes28, 30 of the stacked type piezoelectric/electrostrictive element 24. If(1−Lb/La) is not more than 0.4, it is impossible to make largedisplacement. When (1−Lb/La) is 0.5 to 0.8, it is easy to successfullyachieve both the displacement and the resonance frequency. However, inthis case, it is more appropriate to use a structure in which thestacked type piezoelectric/electrostrictive element 24 is formed on onlyone thin plate section 16 a. This fact also holds when the part of thepiezoelectric/electrostrictive element 24 is located at the movablesection 20.

It is preferable that the total thickness of the stacked typepiezoelectric/electrostrictive element 24 is not less than 40 μm. If thetotal thickness is less than 40 μm, it is difficult to bond the stackedtype piezoelectric/electrostrictive element 24 to the thin plate section16 a. It is desirable that the total thickness is not more than 180 μm.If the total thickness exceeds 180 μm, it is difficult to realize acompact size of the piezoelectric/electrostrictive device 10B.

As for the portion of the stacked type piezoelectric/electrostrictiveelement 24 to make contact with the thin plate section 16 a, when themetal such as brazing material and solder layer is used as the adhesive202, it is preferable that the electrode film exists at the lowermostlayer in view of the wettability as shown in FIGS. 28 and 29. FIGS. 28and 29 show the state in which the electrode film for constructing thesecond electrode 30 is arranged.

When the stacked type piezoelectric/electrostrictive element 24 as shownin FIG. 26 and FIG. 28 is bonded to the thin plate section 16 a by theaid of the metal layer such as the brazing material and the solderlayer, it is preferable to chamfer the angular portion at which at leastone electrode 28 exists, of the lower surface of the stacked typepiezoelectric/electrostrictive element 24 as shown in FIG. 27 and FIG.29, because of the following reason. That is, it is intended to preventthe pair of electrodes 28, 30 from formation of short circuit whichwould be otherwise formed via the metal layer and the thin plate section16 a. FIG. 27 is illustrative of a case in which two angular portions,at which the pair of electrodes 28, 30 exist, are chamfered. FIG. 29 isillustrative of a case in which an angular portion, at which the firstelectrode 28 exists, is chamfered.

Those preferably used as the adhesive 202 for bonding the stacked typepiezoelectric/electrostrictive element 24 to the thin plate section 16 aand the adhesive 200 for bonding the thin plate sections 16 a, 16 b, forexample, to the fixation section 22 include two-part type reactiveadhesives such as those based on epoxy and isocyanate, instantaneousadhesives such as those based on cyanoacrylate, and hot melt adhesivessuch as those based on ethylene-vinyl acetate copolymer. Especially, itis preferable to use those having Shore D hardness of not less than 80as the adhesive 202 for bonding the stacked typepiezoelectric/electrostrictive element 24 to the thin plate section 16a.

It is desirable that an organic adhesive containing a filler such asmetal and ceramics is used as the adhesive 202 for bonding the thinplate section 16 a, 16 b and the piezoelectric/electrostrictive element24 (24 a, 24 b). In this case, it is desirable that the thickness of theadhesive 202 is not more than 100 μm, because of the following reason.That is, when the filler is contained, then the substantial thickness ofthe resin component is decreased, and it is possible to maintain a highhardness of the adhesive.

It is also preferable to use inorganic adhesives as the adhesive 200,202, other than the organic adhesives described above. The inorganicadhesive includes, for example, glass, cement, solder, and brazingmaterial.

On the other hand, as for the shape and the material quality for thethin plate sections 16 a, 16 b, it is enough to have the flexibility,with the mechanical strength of such a degree that no breakage is causeddue to bending deformation. Metal is preferably adopted. In this case,as described above, it is preferable to use a metal material which hasthe flexibility and which is capable of the bending displacement.Specifically, it is preferable to use a metal material which has aYoung's modulus of not less than 100 GPa.

Preferably, it is desirable that the thin plate section 16 a, 16 b ismade of an iron-based material such as various spring steel materials,marageing stainless steel materials, and stainless steel materialsincluding, for example, austenite-based stainless steel materials suchas SUS301, SUS304, AISI653, and SUH660, ferrite-based stainless steelmaterials such as SUS430 and SUS434, maltensite-based stainless steelmaterials such as SUS410 and SUS630, and semiaustenite-based stainlesssteel materials such as SUS631 and AISI632. Alternatively, it isdesirable that the thin plate section 16 a, 16 b is made of anon-ferrous material such as superelastic titanium alloy represented bytitanium-nickel alloy, brass, cupronickel, aluminum, tungsten,molybdenum, beryllium copper, phosphor bronze, nickel, nickel-ironalloy, and titanium.

Next, explanation will be made with reference to FIGS. 32 to 40 forseveral production methods for manufacturing thepiezoelectric/electrostrictive device 10B according to the secondembodiment.

In the third production method, as shown in FIG. 32, a rectangular hole252 having a size of width: 1 mm×length: 8 mm is firstly bored through acentral portion of a stainless steel plate 250 having a size of width:1.6 mm×length: 10 mm×thickness: 0.9 mm to manufacture a substrate 258having a rectangular annular structure with support sections 254, 256arranged on both sides of the hole 252 respectively.

After that, as shown in FIG. 33, a first stainless steel thin plate 260having a size of width: 1.6 mm×length: 10 mm×thickness: 0.05 and asecond stainless steel thin plate 262 having a size of width: 1.6mm×length: 10 mm×thickness: 0.02 (see FIG. 35) are prepared.

After that, as shown in FIG. 33, the adhesive 202 (for example, anadhesive made of epoxy resin) is formed by the screen printing on aportion of the upper surface of the first stainless steel thin plate 260on which the stacked type piezoelectric/electrostrictive element 24 isformed. After that, as shown in FIG. 34, the stacked typepiezoelectric/electrostrictive element 24 is bonded to the firststainless steel thin plate 260 by the aid of the adhesive 202.

After that, as shown in FIG. 35, the adhesive 200 (for example, anadhesive made of epoxy resin) is formed by the screen printing on therespective support sections 254, 256 of the substrate 258.

After that, the first stainless steel thin plate 260, on which thestacked type piezoelectric/electrostrictive element 24 has been alreadyformed, is bonded to the first surface of each of the support sections254, 256 by the aid of the adhesive 200. The second stainless steel thinplate 262 is bonded to the second surface of each of the supportsections 254, 256 by the aid of the adhesive 200. Further, the pressureis applied to the first and second stainless steel thin plates 260, 262in a direction to interpose the substrate 258 to manufacture a masterdevice block 270 shown in FIG. 36. The applied pressure is 0.1 to 10kgf/cm².

After that, as shown in FIG. 36, the master device block 270 is cut intoportions along cutting lines 272 to divide the block into the individualpiezoelectric/electrostrictive devices 10B as shown in FIG. 25. Thecutting process was performed by using a wire saw having a wire diameterof 0.1 mm and a spacing distance of 0.2 mm. When the wire saw is used,it is possible to prescribe substantially the same size for the width ofthe piezoelectric/electrostrictive element 24, the width of the thinplate section 16 a, and the width of the adhesives 200, 202, althoughthese components are made of different materials respectively.

Next, in the fourth production method, as shown in FIG. 37, arectangular hole 252 having a size of width: 1 mm×length: 8 mm is boredthrough a central portion of a stainless steel plate 250 having a sizeof width: 1.6 mm×length: 10 mm×thickness: 0.9 mm to manufacture asubstrate 258 having a rectangular annular structure with supportsections 254, 256 arranged on both sides of the hole 252 respectively.The substrate is 1 mm long.

After that, the adhesive 200 (for example, an adhesive made of epoxyresin) is formed by the screen printing on the respective supportsections 254, 256 of the substrate 258.

After that, as shown in FIG. 38, a first stainless steel thin plate 260having a size of width: 1.6 mm×length: 10 mm×thickness: 0.05 is bondedto the first surface of each of the support sections 254, 256 by the aidof the adhesive 200. A second stainless steel thin plate 262 having asize of width: 1.6 mm×length: 10 mm×thickness: 0.02 is bonded to thesecond surface of each of the support sections 254, 256 by the aid ofthe adhesive 200. Further, the pressure is applied to the first andsecond stainless steel thin plates 260, 262 in a direction to interposethe substrate 258. The applied pressure is 0.1 to 10 kgf/cm².

After that, the adhesive 202 (for example, an adhesive made of epoxyresin) is formed by the screen printing on a portion of the uppersurface of the first stainless steel thin plate 260 on which the stackedtype piezoelectric/electrostrictive element 24 is formed.

After that, as shown in FIG. 40, the stacked typepiezoelectric/electrostrictive element 24 is bonded to the firststainless steel thin plate 260 by the aid of the adhesive 202 tomanufacture a master device block 270.

After that, as shown in FIG. 36, the master device block 270 is cut intoportions along cutting lines 272 to divide the block into the individualpiezoelectric/electrostrictive devices 10B as shown in FIG. 25.

A part (for example, the fixation section 22) of thepiezoelectric/electrostrictive device 10B produced in accordance withthe third and fourth production methods was fixed. A bias voltage of 15V and a sine wave voltage of ±15 V were applied between the pair ofelectrodes 28, 30 of the stacked type piezoelectric/electrostrictiveelement 24 to measure the displacement of the movable section 20. As aresult, the displacement was ±1.2 μm. The frequency was swept with asine wave voltage of ±0.5 V to measure the minimum resonance frequencyto exhibit the maximum displacement. As a result, the minimum resonancefrequency was 50 kHz.

In the third and fourth production methods described above, thesubstrate 258 is constructed to have the rectangular annular structurehaving the support section 254 to be formed into the movable section 20thereafter and the support section 256 to be formed into the fixationsection 22 thereafter. Alternatively, as shown in FIG. 41, a rectangularannular structure is also available, in which a hole 252 is widened tohave a frame-shaped section 254 a for supporting first and secondstainless steel thin plates 260, 262 (section for substantially definingthe thickness of a portion to allow at least the movable section 20 tointervene thereafter) and a support section 256 to be formed into thefixation section 22 thereafter.

In this case, the substrate 258 is secured by the aid of the adhesive200 so that the substrate 258 is interposed between the first and secondstainless steel thin plates 260, 262 to manufacture a master deviceblock 270 similar to one shown in FIG. 36, followed by being cut alongcutting lines 272 as shown in FIG. 36. Accordingly, as shown in FIG. 44,for example, it is possible to produce a piezoelectric/electrostrictivedevice in which the movable section 20 does not exist between theforward ends of the thin plate sections 16 a, 16 b.

Alternatively, another production method is available, for example, asshown in FIG. 44. The adhesive 200 and the fixation section 22 arearranged between the rearward ends of the respective thin plate sections16 a, 16 b respectively. The adhesive 200, the movable section 20, and apressurizing spacer 310 are arranged between the forward ends of therespective thin plate sections 16 a, 16 b respectively as shown bytwo-dot chain lines. After that, for example, the pressure is appliedfrom both sides of the respective thin plate sections 16 a, 16 b.Accordingly, the fixation section 22 is secured between the rearwardends of the respective thin plate sections 16 a, 16 b by the aid of theadhesive 200. The movable section 20 is secured to the forward ends ofthe respective thin plate sections 16 a, 16 b respectively by the aid ofthe adhesive 200. In this arrangement, the pressurizing spacer 310 isnot secured to the movable section 20 by an adhesive or the like.Therefore, the pressurizing spacer 310 can be removed with ease afterthe cutting along cutting lines. In order to adjust the thickness(distance between the fixation section 22 and each of the thin platesections 16 a, 16 b) between the fixation section 22 and each of thethin plate sections 16 a, 16 b, a second fixation section (not shown),which has approximately the same thickness as that of the movablesection 20, may be fixed on both sides thereof between the fixationsection 22 and each of the thin plate sections 16 a, 16 b by the aid ofthe adhesive 200.

Next, explanation will be made with reference to FIGS. 42 to 46 for afifth production method which is different from the third and fourthproduction methods described above.

The fifth production method is also applicable to a case in whichsupport sections 254, 256 are bonded to a first stainless steel thinplate 260 and a second stainless steel thin plate 262 to manufacture amaster device block 270 in the same manner as in the third and fourthproduction methods described above, followed by being divided intoindividual piezoelectric/electrostrictive devices. The fifth productionmethod is also applicable to a case in which thepiezoelectric/electrostrictive device 10B is produced such that a unit,which is formed in a separate manner to give each actuator section 204comprising the stacked type piezoelectric/electrostrictive element 24 a,24 b formed on the thin plate section 16 a, 16 b, is secured to thefixation section 22 which is prepared in a separate manner as well.

In the following description, the support section 256 to be formed intothe fixation section 22 thereafter and the fixation section 22 areconveniently referred to as “fixation section 22”, and the first andsecond stainless steel thin plates 260, 262 to be formed into the thinplate sections 16 a, 16 b thereafter and the thin plate sections 16 a,16 b are conveniently referred to as “thin plate sections 16 a, 16 b”.

As shown in FIG. 42, when the thin plate sections 16 a, 16 b are bondedby the aid of the adhesive 200 to the fixation section 22, if theadhesive having fluidity is used, then it is preferable to provide bumps280 am, 280 bm for the respective thin plate sections 16 a, 16 b inorder to define the places for forming the adhesive 200. Of course, whenthe adhesive having high viscosity is used, it is unnecessary to providesuch a bump. In this example, assuming that the adhesive having fluidityis used when an unillustrated object is bonded between the open ends ofthe respective thin plate sections 16 a, 16 b, bumps 280 an, 280 bn arealso provided on the mutually opposing surfaces of the open ends of therespective thin plate sections 16 a, 16 b. The bumps 280 am, 280 an, 280bm, 280 bn may be also formed by stacking plate-shaped members.

FIG. 43 is illustrative of a case in which the adhesive having highviscosity is used as the adhesive 200 for bonding the fixation section22 and the respective thin plate sections 16 a, 16 b, wherein the bump280 am, 280 bm as described above is not provided at portions to whichthe fixation section 22 is bonded.

FIG. 44 is illustrative of a case in which the adhesive having highviscosity is commonly used as the adhesive 200 for bonding the fixationsection 22 and the respective thin plate sections 16 a, 16 b, depictinga structure in which the bump 280 am, 280 bm as described above is notprovided. In this example, assuming that the adhesive having highviscosity is used when an unillustrated object is bonded between theopen ends of the respective thin plate sections 16 a, 16 b, the bump 280an, 280 bn is not provided on the mutually opposing surfaces of the openends of the respective thin plate sections 16 a, 16 b as well.

FIG. 45 is illustrative of a case in which the adhesive having highfluidity is commonly used as the adhesive 200 for bonding the fixationsection 22 and the respective thin plate sections 16 a, 16 b, especiallydepicting an example which is provided with projections 282 am, 282 bmfor comparting regions for forming the adhesive 200 on the respectivethin plate sections 16 a, 16 b. In this example, assuming that theadhesive having fluidity is used when an unillustrated object is bondedbetween the open ends of the respective thin plate sections 16 a, 16 b,projections 282 an, 282 bn are also provided on the mutually opposingsurfaces of the open ends of the respective thin plate sections 16 a, 16b.

As shown in FIG. 46 concerning the example shown in FIG. 42, it is alsopreferable that the size of the fixation section 22, especially theareal size of the surface of each of the thin plate sections 16 a, 16 bopposed to the bump 280 is made to be larger than the areal size of thebump 280 am, 280 bm. Accordingly, for example, the substantial drivingportion (portion between the bumps 280 am and 280 an and portion betweenthe bumps 280 bm and 280 bn) of the thin plate sections 160 a, 160 b canbe defined by the bump 280 am, 280 bm. As shown in FIG. 42, when theareal size of the surface of each of the thin plate sections 16 a, 16 bopposed to the bump 280 am, 280 bm concerning the fixation section 22 ismade to be substantially the same as the areal size of the bump 280 am,280 bm, it is feared that the dispersion in size concerning the fixationsection 22 and the bump 280 am, 280 bm affects the length of thesubstantial driving portion. FIG. 46 is illustrative of the case inwhich the size of the fixation section 22 is increased toward the openends of the thin plate sections 16 a, 16 b. Alternatively, the size ofthe fixation section 22 may be increased in a direction opposite to thedirection described above.

In FIGS. 42 to 46, the bumps 280 am, 280 bm, 280 an, 280 bn or theprojections 282 am, 282 bm, 282 an, 282 bn are integrated with the thinplate sections. However, these components may be provided by laminatingappropriately processed plates by the aid of an adhesive, in the samemanner as in FIG. 19 or FIG. 23. In the case of the provision by meansof the integration, the bumps 280 am, 280 bm, 280 an, 280 bn or theprojections 282 am, 282 bm, 282 an, 282 bn can be integrally providedsimultaneously with the formation of the thin plate sections 16 a, 16 bby thinning the plate-shaped member, for example, by means of etching orcutting.

The embodiment described above is illustrative of the case in which theadhesive 200, 202 is formed by means of the screen printing.Alternatively, it is possible to use, for example, dipping, dispenser,and transfer.

Next, explanation will be made with reference to FIGS. 47 to 52 forvarious illustrative constructions concerning the adhesive 202 whichintervenes between the thin plate section 16 a and the stacked typepiezoelectric/electrostrictive element 24 and the adhesive 200 whichintervenes between the respective thin plate sections 16 a, 16 b and thefixation section 22.

At first, in the first technique shown in FIG. 47, a large number ofholes 290 are provided through the thin plate section 16 a. The stackedtype piezoelectric/electrostrictive element 24 is bonded to a portion atwhich the holes 290 are provided, by the aid of the adhesive 202. Inthis arrangement, the adhesive 202 enters the inside of the holes 290.Therefore, the adhesion area is substantially increased, and it ispossible to use a thin thickness of the adhesive 202. It is preferablethat the thickness of the adhesive 202 is not more than 5% of the totalthickness of the stacked type piezoelectric/electrostrictive element 24and not less than a thickness of such a degree that the thermal stressdue to the difference in coefficient of thermal expansion between thethin plate section 16 a and the adhesive 202 can be absorbed.

It is preferable that the diameter of the hole 290 is 5 μm to 100 μm.The arrangement pattern may be either a matrix form or a zigzagarrangement. Of course, a plurality of holes 290 may be arranged in onearray. It is preferable that the arrangement pitch of the holes 290 is10 μm to 200 μm. Alternatively, recesses (bores) may be used in place ofthe holes 290. In this arrangement, it is preferable that the diameterof the bore is 5 μm to 100 μm. The arrangement pattern may be either amatrix form or a zigzag arrangement. It is preferable that thearrangement pitch of the bores is 10 μm to 200 μm. Especially, in thecase of the recess (bore), for example, it is also preferable to use arectangular configuration as viewed in plan view with its opening areawhich is slightly smaller than the projection area of thepiezoelectric/electrostrictive element 24 onto the thin plate section 16a. Those adoptable as the technique for forming the holes 290 or thebores in the thin plate section 16 a include, for example, etching,laser machining, stamping or punching out, drill machining, electricdischarge machining, and ultrasonic machining.

In the second technique shown in FIG. 48, the surface 292 of a portionof the thin plate section 16 a, on which the stacked typepiezoelectric/electrostrictive element 24 is formed, is roughened bymeans of the blast treatment, the etching treatment, or the platingtreatment. In this arrangement, the lower surface 294 of the stackedtype piezoelectric/electrostrictive element 24 is also roughened.Accordingly, the adhesion area is substantially increased. Therefore, itis possible to use a thin thickness of the adhesive 202.

FIG. 48 is illustrative of the case in which the surface of the thinplate section 16 a and the lower surface of thepiezoelectric/electrostrictive element 24 (surface opposed to the thinplate section 16 a) are roughened. However, it is enough that thesurface having the small adhesion force with respect to the adhesive 202is roughened. A sufficient effect is obtained, for example, even whenonly the surface of the thin plate section 16 a is roughened. Thesurface roughness is preferably Ra=0.1 μm to 5 μm, and more preferably0.3 μm to 2 μm, for example, as estimated by the center line averageroughness.

In the third technique shown in FIG. 49, a curvature 296 is provided forthe stick-out shape of the adhesive 200, especially for the stick-outshape of the adhesive 200 toward the inner wall 22 a of the fixationsection 22. In this arrangement, it is preferable that the radius ofcurvature is not less than 0.05 mm so that the stick-out shape islinear, or the stick-out shape includes a linear portion. The formationof the curvature 296 for the stick-out portion of the adhesive 200 canbe realized, for example, by inserting a cylindrical core member intothe space formed by the thin plate sections 16 a, 16 b and the innerwall 22 a of the fixation section 22, before curing the adhesive 200.Practically, the control is made based on the use of the applicationamount and the physical property of the adhesive 200 so that thestick-out shape is at least not convex.

Accordingly, the inner wall 22 a of the fixation section 22 and theinner walls of the respective thin plate sections 16 a, 16 b are alsoused as the adhesion surfaces. Therefore, the adhesion area isincreased, and it is possible to increase the adhesion strength.Further, it is possible to effectively disperse the concentration of thestress on the joined portions (angular portions) between the inner wall22 a of the fixation section 22 and the inner walls of the respectivethin plate sections 16 a, 16 b.

In the fourth technique shown in FIG. 50, angular portions of the innerwall 22 a of the fixation section 22 are chamfered respectively to formtapered surfaces 298. The stick-out amount of the adhesive 200 can bestabilized by appropriately adjusting the radius of curvature and theangle of the chamfering. It is possible to suppress the local dispersionof the adhesion strength, and it is possible to improve the yield.

The following method is preferably used to chamfer the angular portion.That is, for example, the cutting and the polishing are performedbeforehand for the portions to be formed into the angular portions ofthe support section 256 to form the tapered surfaces 298 before theassembling. Of course, the chamfering may be performed after theassembling. In this case, for example, the laser machining, theultrasonic machining, or the sandblast is preferably adopted.

The fifth technique shown in FIG. 51 relates to the punching out processwhich is usually performed, for example, when the thin plate sections 16a, 16 b are manufactured. In this case, burrs 300 are formed. The formedburrs 300 may be removed before the assembling. However, they may beallowed to remain as they are. In this case, it is preferable that thedirections of the formed burrs 300 are regulated, for example, inconsideration of the handling and the adhesion directions of therespective members as well as the easiness of control of the amount ofthe adhesive. The example shown in FIG. 51 is illustrative of a state inwhich the burrs 300 of the thin plate sections 16 a, 16 b are directedoutwardly.

In the sixth technique shown in FIG. 52, as described above, thethickness of the portion to be formed into the first thin plate section16 a thereafter is made to be larger than the thickness of the portionto be formed into the second thin plate section 16 b thereafter. In thecase of the use as the actuator section 204, the stacked typepiezoelectric/electrostrictive element 24 is preferably formed on thefirst thin plate section 16 a. In the case of the use as the sensor, thestacked type piezoelectric/electrostrictive element 24 is preferablyformed on the first thin plate section 16 a as well.

Other techniques are also available. For example, when the stacked typepiezoelectric/electrostrictive element 24 is bonded to the thin platesection 16 a, 16 b by the aid of the adhesive 202, for example, it isalso preferable that a ZrO₂ layer is allowed to intervene as anunderlying layer for the lower surface of the stacked typepiezoelectric/electrostrictive element 24.

When the stainless steel thin plates 260, 262 (see; for example, FIG.33) are used as the thin plate sections 16 a, 16 b, it is preferablethat the longitudinal direction of the thin plate sections 16 a, 16 b isapproximately coincident with the direction of the cold rolling appliedto the stainless steel thin plates 260, 262.

It is preferable that the piezoelectric/electrostrictive layer 26 forconstructing the stacked type piezoelectric/electrostrictive element 24is stacked in about three layers to ten layers.

The piezoelectric/electrostrictive devices 10A, 10B described above canbe utilized as the active device including, for example, varioustransducers, various actuators, frequency region functional parts(filters), transformers, vibrators, resonators, oscillators, anddiscriminators for the communication and the power generation, as wellas the sensor element for various sensors including, for example,ultrasonic sensors, acceleration sensors, angular velocity sensors,shock sensors, and mass sensors. Especially, thepiezoelectric/electrostrictive devices 10A, 10B described above can bepreferably utilized for various actuators to be used for the mechanismfor adjusting the displacement and the positioning and for adjusting theangle for various precision parts such as those of optical instrumentsand precision mechanical equipments.

It is a matter of course that the piezoelectric/electrostrictive deviceand the method for producing the same according to this invention arenot limited to the embodiments described above, which may be embodied inother various forms without deviating from the gist or essentialcharacteristics of this invention.

1. A piezoelectric/electrostrictive device, comprising: a pair ofmutually opposing vibration plates, each extending in a longitudinaldirection of said device and having a width extending within a planethereof substantially perpendicular to said longitudinal direction, eachof said vibration plates having a first portion and a second portion; afixation section joined to said first portion of each of said vibrationplates; and at least one piezoelectric/electrostrictive element arrangedon at least one of said vibration plates, such that only a singlepiezoelectric/electrostrictive element exists across the width of saidat least one of said vibration plates, wherein a surface of said devicebetween said fixation section and said second portion of at least one ofsaid vibration plates is curved.
 2. The piezoelectric/electrostrictivedevice according to claim 1, wherein said surface of said device alsoextends between said fixation section and said second portion of theother one of said vibration plates.
 3. Thepiezoelectric/electrostrictive device according to claim 1, wherein amovable section is provided at ends of said second portions of said pairof vibration plates.
 4. The piezoelectric/electrostrictive deviceaccording to claim 3, wherein at least one of said movable section andsaid fixation section has mutually opposing end surfaces.
 5. Thepiezoelectric/electrostrictive device according to claim 4, wherein saidpiezoelectric/electrostrictive device has such a structure that internalresidual stress, which has been generated in at least one of said thinplate section and said piezoelectric/electrostrictive element duringproduction, is released by forming said mutually opposing end surfaces.6. The piezoelectric/electrostrictive device according to claim 3,wherein any one of said movable section and said fixation section has acutoff section and a part of said cutoff section constitutes mutuallyopposing end surfaces of said movable section and said fixation section.7. The piezoelectric/electrostrictive device according to claim 6,wherein a gap is formed between said mutually opposing end surfaces. 8.The piezoelectric/electrostrictive device according to claim 6, furthercomprising a member interposed between and attached to at least one ofsaid mutually opposing end surfaces, said member being formed from thesame material as any one of said movable section and said fixationsection, and an areal size of a surface of said member interposedbetween said end surfaces is substantially the same as an areal size ofsaid end surfaces.
 9. The piezoelectric/electrostrictive deviceaccording to claim 6, further comprising a plurality of membersinterposed between said mutually opposing end surfaces, said pluralityof members being formed from a material that is different from any oneof said movable section and said fixation section, and an areal size ofthe surfaces of said plurality of members interposed between said endsurfaces are substantially the same as an areal size of said endsurfaces.
 10. The piezoelectric/electrostrictive device according toclaim 9, wherein at least one member of said plurality of members is anorganic resin.
 11. The piezoelectric/electrostrictive device accordingto claim 1, wherein said piezoelectric/electrostrictive elementcomprises a piezoelectric/electrostrictive operating portion positionedon an outer surface of said at least one vibration plate beginning at aposition overlapping said fixation section and extending onto at least aportion of said at least one vibration plate.
 12. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidpiezoelectric/electrostrictive element is in the shape of a film, and issecured to said vibration plate by the aid of an adhesive.
 13. Thepiezoelectric/electrostrictive device according to claim 12, whereinsaid piezoelectric/electrostrictive element comprises apiezoelectric/electrostrictive layer and a pair of electrodes formed onsaid piezoelectric/electrostrictive layer.
 14. Thepiezoelectric/electrostrictive device according to claim 13, whereinsaid piezoelectric/electrostrictive element is constructed in a stackedform comprising a plurality of units each including saidpiezoelectric/electrostrictive layer and said pair of electrodes. 15.The piezoelectric/electrostrictive device according to claim 1, whereinsaid curved surface has a radius of curvature of at least 0.05 mm. 16.The piezoelectric/electrostrictive device according to claim 1, furthercomprising an adhesive between said fixation section and said firstportion of each of said vibration plates.
 17. Thepiezoelectric/electrostrictive device according to claim 1, wherein saidvibration plates comprise metal.